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Class 

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CopyrightN . 



COPYRIGHT DEPOSIT 



ELEMENTARY 
PHYSICAL GEOGRAPHY 



elementary 
Physical Geography 

AN OUTLINE OF PHYSIOGRAPHY 



JACQUES W. REDWAY 

II 



1 ' 772g waste of the Old Land is the material of the New ' ' 



NEW YORK 

CHARLES SCRIBNER'S SONS 

1908 



LIBRARY of CONFESS 
IwO CODH* H«Wl»d« 

MAY 20 1908 
Mac, 6> "tel 

QOFY *' 
2. d fr 7 3/ 



Copyright, 1900, 1908, by 
JACQUES W. REDWAY 




PREFACE 

The science of Geography sets forth the relations of life 
and its environment to the earth, and it is the function of 
both the writer and the teacher of geography to explain 
these relations. In the elementary geography the pupil 
studies the various peoples of the earth and the countries 
in which they live; in the advanced geography there is 
presented in addition a discussion of the industries of life 
and their geographic distribution. The present volume, 
is designed to show that the distribution of life is gov- 
erned very largely by the conditions of geographic environ- 
ment, and that human history and industries are alwaj^s 
closely connected with geographic laws — in many instances 
the direct resultants of them. 

The science of Geography as now understood includes 
something more than a mere description of topographic 
forms — it comprehends the gradual and progressive devel- 
opment of these forms and their results as regards life, 
as well. It includes also the effects of temperature and 
moisture, for life and its activities depend also on them. 
That is, it naturally involves the principles of descriptive 
geography, physiography, and economics; and this vol- 
ume is designed to show their interrelation. 

In scope this book contains all the principles recom- 
mended by the Committee of Fifteen, and such other feat- 
ures as have suggested . themselves to the author. It is 
designed to be used in the junior grades of the High School, 



vi PREFACE 

and in Normal Schools. The arrangement of the subjects 
is logical, but the teacher may readily organize a course 
of study in the subject without reference to the present 
arrangement. To make this more easily accomplished, 
the principles of the subject are set forth in the larger 
type; relevant matter that is illustrative but non-essential 
is presented in smaller type. In general, the teacher should 
not hesitate to omit a topic, the discussion of which is too 
difficult for the class. 

In this edition the notes are inserted in connection with 
the text and a brief laboratory manual is added to the 
appendix. There is no change in the arrangement of 
chapters, and none in the sequence of topics except as 
noted. 

The Questions and Exercises are designed to stimulate 
observation and independent thought. 

In the preparation of the new edition I take pleasure 
in acknowledging the most valuable counsel of Principal 
Myron T. Pritchard, Everett School, Boston. 

The books designated for reference and collateral read- 
ing are intentionally few in number, and those most com- 
monly cited should be in the school library. The teacher 
will also find it very advisable to keep in close touch with 
the publications of the United States Geological Survey, 
and the Weather Bureau. 

J. W. It. 



CONTENTS 



PAGE 

Introductory 1 

CHAPTER 

I. The Earth Among Planets ...".. 9 
II. The Structure, of the Earth . . . . . 21 

III. Land and Water, and Their Outlines . . 42 

IV. The Results of Slow Movements of the Rock 

Envelope: Plains, Plateaus, and Mountains . 60 

V. Destructive Movements of the Rock Envelope: 

Volcanoes and their Phenomena ... 85 

VI. Destructive Movements of the Rock Envelope: 

Earthquakes . . . .• . . . .100 

VII. The Wasting of the Land : The Work of Rivers .. Ill 

VIII. The Wasting of the Land : The Work of Under- 
ground Waters 137 

IX. The Wasting of the Land: The Work of Ava- 
lanches and Glaciers 154 

X. The Wasting of the Land: The Results of Im- 
perfect and Obstructed Drainage : Lakes and 
Marshes 170 

XI. Ocean Waters and their Movements: Waves, 

Tides, and Currents 193 

XII. The Atmosphere and its Properties: Winds . 214 

XIII. The Moisture of the Atmosphere : Seasonal and 

Periodical Distribution of Rainfall . .231 

XIV. The Moisture of the Atmosphere: Cyclonic 

Storms 248 

vii 



viii CONTENTS 

CHAPTER PAGE 

XV. Electrical and Luminous Phenomena of the 

Atmosphere . 258 

XVI. Climate and its Factors 286 

XVII. The Dispersal of Life .' 302 

XVIII. Geographic Distribution of Plants and Animals 314 

XIX. Man 334 

XX. The Industrial Regions of the United States 352 

Appendix 375 

Index 3X1 



LIST OF MAPS AND PLATES 

PAGE 

The Solar System (Colored) 11 

Photograph of a Part of the Moon 12 

Order of Strata 35 

North America in Archjean Times 36 

North America in Cenozoic Era 37 

United States in Quaternary Age 38 

Land and Water Hemispheres 41 

Elevation of Land and Depth of Oceans (Colored) 44, 45 

Stretch of Norway Coast 46 

Barrier Beaches of Carolina Coast 55 

Plateaus of the Colorado River 69 

Distribution of Volcanoes (Colored) . . . - . 99 

Loops and Cut-offs of the Lower Mississippi . .114 

Palmyra Bend, Mississippi River 116 

Delta of the Mississippi River . . . . . .122 

Chesapeake Bay— A "Drowned" Valley .... 123 

River Systems and Drainage (Colored) . . . 134, 135 

Glaciated Region of the United States . . . .164 

Marsh Lakes of Florida . . . . . . .171 

Lagoons of Martha's Vineyard 174 

Lake St. Clair 180 

ix 



x LIST OF MAPS AND PLATES 

PAGE 

Lake Bonneville and its Remnants 181 

Section Along the Great Lakes 1S3 

Chart of Co-tidal Lines 203 

Ocean Currents (Colored) 205 

Prevailing Winds of the Atlantic 219 

Chart of Winds (Colored) 223 

Distribution of Rain (Colored) 240 

Storm Maps — First and Second Days (Colored) . . 265 

Chart of Magnetic Isogonics 277 

Isotherms — January and July (Colored) .... 293 

Distribution of Animals (Colored) 318 

Distribution of Vegetation (Colored) .... 326 

Races of Man (Colored) 339 

Physical Map of the United States (Colored) . . 353 

New York Harbor and its Approaches (Colored) . 369 



ELEMENTARY 
PHYSICAL GEOGRAPHY 



PHYSICAL GEOGRAPHY 

INTRODUCTORY 

Only a casual thought is needed to make it apparent 
that life on the earth, as we now find it, depends on a very- 
delicate adjustment to its surroundings. Living beings 
require certain conditions of heat, moisture, and geo- 
graphic environment; and if these are changed ever so 
slightly the life forms must adjust themselves to the new 
conditions, or else they must seek a new abiding-place; 
or, perhaps, they may perish altogether. 

For instance, turf grass requires water at very short 
intervals, and if for several successive years there are 
droughts five or six months in duration, it will die. And 
if there are herds of cattle in the region, they must adjust 
themselves to the changed conditions. They must adapt 
themselves to other food, or they must migrate. Other- 
wise they too will perish. 

Were the temperature of the earth to change only a few 
degrees there would be a similar disturbance that would 
involve almost every living thing. And if it should fall so 
low that the water were everywhere frozen, life as we now 
know it could not exist any great length of time, because 
living beings need in their structure a large proportion of 
water, and the latter must be taken into the structure in 
a liquid form. For a similar reason, if all the water were 
in the form of vapor, life could not long endure unless the 



PHYSICAL GEOGRAPHY 



life forms were very different in structure from those with 
which we are acquainted. 

Life is by no means evenly distributed over the earth, 
however. A few species spend the greater part of their 
existence in the air, and a larger number live in water only. 
By far the greater number of species, moreover, live at the 
plane of contact between the atmosphere and the earth's 




A FERTILE VALLEY, NEW YORK 
Capable of producing abundant foodstuffs, and densely peopled. 

rock envelope — that is, on the land surface of the earth. 
Their distribution is governed by the conditions of warmth, 
moisture, and surface, and if these conditions were to 
change ever so slightly, the distribution would be disturbed. 
Life and its distribution are governed by geographic laws; 
if the latter change, so must the former. 

Man, who stands at the head of animate nature, is able 



INTRODUCTORY 3 

to endure a much wider range of warmth, moisture, and. 
surface features than most other living beings. He can 
withstand extremes of heat and cold that are fatal to most 
other animals, and he can live indifferently in places of 
great drought or of excessive moisture. The arctic re- 
gions are not so cold, nor the tropical lands so hot that 
man cannot dwell there; and throughout the wide world 
one can find scarcely an ice-clad summit or a sun-beaten 
desert in which human beings have not lived. 

On account of these varying conditions — all the result of 
geographic laws — the study of the earth is both important 
and interesting, because it is the home of man. Like all 
forms of life, man requires food; more than any other ani- 
mal, he needs shelter. His food, of which he consumes 
about eighty tons during the three or four score years of 
his existence, comes from the earth — the land, the water, 
and the air each yielding part — and the materials that are 
used for clothing and shelter come also from the same 
source — the earth. 

So, in order to understand the story of life, its history 
and its industries, one must learn about the physical geog- 
raphy of its surroundings — that is, about its environment, 
or the various conditions of heat, moisture, and surface 
features. Land animals could not live until the waters 
were separated from the land. Before they could main- 
tain life, vegetation must have spread itself over the land; 
and before vegetation could endure, there must have been 
soil. And before there could be soil, the surface of the 
land must have been folded, broken, worn, and furrowed, 
so that the fragments of rock could be ground fine and 
formed into soil. All these earth-weathering processes 
must have been going on before the higher forms of life 



PHYSICAL GEOGRAPHY 



could exist, and all over the surface of the land such 
changes are even now going on from day to day. Scarcely 
a summer shower falls that does not leave its marks; and, 
indeed, throughout the physical history of the earth the 
most apparent feature is constant change. 

From the time the land was first divided from the waters, 
the continents, or great bodies of land, have been ever 




ARCTIC LANDS 
Too cold and not enough soil jor the support oj Hie. 

changing. In places, alternately sinking, rising, :unl 
warping in various ways, the shore outlines have taken 
various forms. Rugged coasts sinking below sea-level 
have resulted in the fjorded shores, such as those of the 
North Atlantic States, making the harbors where so much 
of the manufacture and commerce of the country have 
centred. Rising coasts have lifted natural harbors above 
sea-level, making the approaches to the land so difficult 



INTRODUCTORY 5 

that vessels can find no sheltered anchorage. Old sea- 
bottoms, covered with sediments that form the richest 
soil, have been lifted above the sea, and in time have be- 
come densely peopled areas. 

Certain forces are causing the surface of the rock en- 
velope to wrinkle and fold, forming plateaus, mountains, 
and valleys; and at the same time the waters of the atmos- 
phere, falling as rain or snow, are constantly at work wear- 
ing away the wrinkles and folds, carrying the material back 
to the sea. 

It is necessary to know about these processes, and to 
understand how they are going on, because almost every 
form of life is more or less modified by them, and certainly 
the history and the industries of man are very largely gov- 
erned by them. Man may rise superior to his environ- 
ment — that is, his geographic surroundings — but he is al- 
ways more or less modified by it. Mountains and valleys, 
plains and plateaus, oceans and rivers, have all been potent 
factors in making the destiny of peoples. 

The rugged and barren slope of Norway forbade any 
great development of agriculture, while the deeply fjorded 
shores invited the pursuits of the sea. The Norse people, 
therefore, became sea rovers and magnificent sailors. The 
uncultivable mountains of Greece could not well yield the 
food-stuffs necessary for the population, so we find a his- 
tory of "Greece scattered." From the remotest times the 
rich valley of the Tigris and Euphrates, because of its fer- 
tility, has always attracted people, and we therefore find it 
a densety peopled region. 

Unless there is something to unfit them for human habi- 
tation, lowlands are favorite places of dwelling, and by far 
the greater part of the world's population is found in them. 



G 



PHYSICAL GEOGRAPHY 



How is the statement borne out in the case of the Central 
Plain of North America? — the swampy, forest plain of 
the Amazon?— the great lowland region of southeastern 
Asia? — the northern plains of Eurasia? 

River bottom-lands, also, are nearly always densely peo- 




A RUGGED NORWEGIAN SLOPE 
A locality not suitable for farming; a jew food- plants may be grown. 

pled. How is this illustrated in the history of Egypt? — 
with regard to the nations dwelling in the Mesopotamia? 
— the valley of the Ganges? — the bottom-lands of the 
Mississippi River? — the Sacramento-San Joaquin Valley? 
Extensive desert regions are always sparsely peopled; 



INTRODUCTORY 



why? How is this illustrated in the eastern and western 
halves of the United States? The population of rugged 
highlands and mountain ranges is usually sparse; is there 
a good reason therefor? 

The hot regions of the land are almost always densely 
peopled, the deserts and forest swamps excepted. Is this 




A TROPICAL SCENE 
Both temperature and moisture are favorable to a great productivity of food-stuffs. 

true of the intensely cold regions? Life thrives best in 
regions of warmth and of strong sunlight. Are all parts 
of the earth equally warmed? Have all parts the same 
intensity of light? Compare the density of population of 
cold and dimly lighted parts of the earth with that of the 
warm and strongly lighted parts: in which is it greatest? 



S PHYSICAL GEOGRAPHY 

The study of the distribution of heat and cold, of rain 
and drought, of highlands and lowlands, and of fertile and 
infertile regions forms an essential part of the study of 
geography; the study of the progressive changes that have 
been and are now taking place on the earth's surface con- 
stitutes the science of physiography, or "nature-writing." 
The object of this book is to show that the fundamental 
laws of geographic science not only control the structure 
of life forms and their distribution over the earth, but that 
they also largely control and modify the history, the activi- 
ties, and the various economies of man, as well. 

QUESTIONS AND EXERCISES.— What are the leading industries 
of the city or town in which you live? Note and describe a geographic 
feature that favors any one of these industries, and without which the 
industry could not thrive. 

What would be the effect, so far as the habitability of the sur- 
rounding region is concerned, were the rainfall to be diminished one- 
half? 

How would a material change in the surface features affect the in- 
dustries? 

On p. 369 is a map of New York Harbor ; what would be the effect 
on the commerce of the port if the surface of the water were lowered 
two hundred feet? 

Mention two or more reasons why lowland regions are more densely 
peopled than highlands. 

Quito, the capital of Ecuador, is in the midst of a fertile region 
nearly two miles above sea-level; what are its advantages over the 
coast plain region to the westward? 

Make a list of half-a-dozen or more extensive regions that are not 
habitable, and explain the geographic reasons for their condition. 

COLLATERAL READING 

Mill.— Realm of Nature, pp. 331-336. 
Shaler. — Nature and Man in North America. 
Adams. — The New Empire, ohap. I. 
»Fhoude. — History of English Literature — The Saxons. 



CHAPTER I 

THE EARTH AMONG PLANETS 

The Solar System. — The cluster of heavenly bodies 
called the solar system is one of many groups in space. 
The members of this group revolve about a common centre 
of gravity, however, and for this reason they form collec- 
tively a system. 

The members of this system vary greatly in size. The 
largest is about 886,000 miles in diameter, and the small- 
est are probably too minute to be measured by ordinary 
standards. Eight of them are about three thousand 
miles, more or less, in diameter; about four hundred 
vary approximately from ten to five hundred miles in 
diameter. 

The largest member of the solar system, the sun, is 
about eight hundred times as large as all the other members 
together, and the common centre of gravity around which 
the various members revolve is very near to or within it. 
The eight bodies next in size are called planets, and all but 
two of them are attended by one or more satellites or m.oons. 
The four hundred or more small planets are called asteroids, 
or planetoids. There are also several comets and groups 
of meteors which have a permanent place in the solar 
system. , 

The asteroids move in orbits in the space between Mars and Jupiter. 
Many of them do not exceed twenty or thirty miles in diameter, and 

9 



10 PHYSICAL GEOGRAPHY 

the largest probably does not exceed five hundred miles. Their com- 
bined volume is less than one four-thousandth part of the mass of the 
earth. Eros, one of the recently discovered asteroids, has an orbit so 
eccentric that it crosses that of Mars, and at times is nearer to the earth 
than is Mars. 

But little is known about the nature and structure of comets, but 
some of them are composed largely of gaseous matter. One comet, 
Tempel's, undoubtedly consists of a vast swarm of meteors; hut it is 
probable that comets are constituted of different kinds of matter. 
Several of them belong to the solar system, but many are temporary 
visitors, coming from unknown regions of space, whirling around the sun 
and again vanishing into space. 

Meteors, or shooting stars, are small bodies that seem to exist generally 
throughout space. In sweeping through space, the earth and the other 
planets encounter them without number. Most of them on reaching 
the earth's atmosphere are heated to whiteness and are dissipated as 
white-hot vapor. Many of the larger ones reach the earth, and sonic 
of them have been analyzed. They consist mainly of iron and nickel 
in a metallic form, or else of matter not differing materially from lava. 
No element has yet been found in a meteor that does not occur in the 
earth. In one instance gold, in another minute diamonds, were found 
in a meteorite. 

The planets are composed of the same kinds of matter as 
the earth, but they are unlike one another in physical con- 
dition. Some, bulk for bulk, are but little heavier than 
water, others are about as heavy as iron ore. Some of the 
planets have apparently lost the greater part of their heat ; 
still others are very hot. The sun, for instance, is a glowing 
mass at white heat. 

The Sun and the Planets.— The similarity between the 
sun and the planets is very marked. They whirl from 
west to east around a common centre of gravity, and each 
turns or spins on its axis in the same direction. Bach 
is nearly spherical in shape, and is more or loss flattened 
at its poles. So far as is known, each is surrounded by 
an atmosphere. 



THE EARTH AMONG PLANETS 



11 



According to the nebular theory of La Place, which is held by many 
scientists, the members of the solar system formerly existed as a body 
of gaseous matter, or, perhaps, of minute masses. The force of gravity 
drew the particles together, toward the centre of gravity, and a rotation 




THE SOLAR SYSTEM 
The space within (he orbit oj Jupiter shows the relative size oj the Sun 



of the mass around the centre of gravity resulted. Finally, parts of 
the mass were thrown off, one after another in the form of rings, a 
planet developing out of each ring. In a similar manner, the rapid 
rotation of each planet threw off portions of its mass forming the 
satellites. 



12 



PHYSICAL GEOGRAPHY 



The researches of Chamberlain and Moulton, however, make it 
probable that solar systems develop from spiral nebulae, the plaints 
having been formed around nuclei of considerable size. The nuclei, 
in turn, attracted the scattered matter near which it passed. This 
theory, known as the " planetesmal hypothesis," accords with many 
facts not explained by any other theory. 

So far as is known, matter exists in at least three physical forms — 




A PORTION OF THE MOON'S SURFACE 



solid, liquid, and gaseous — and nearly every chemical element and many 
of their compounds may assume each of these forms. In the solid form 
the molecules are bound by a strong cohesion ; in the liquid form they 
are slightly cohesive; in the gaseous form they repel one another. 
Most of the substances that in the earth are solids, in the sun exist as 
white-hot vapors. 

Although the assumed formation of the solar system by either process 
is a matter of theory, both theories are supported by evidence. The 
telescope reveals many such masses of gaseous matter showing planetary 




A SPIRAL NEBULA— CANES VENATICI 



14 PHYSICAL GEOGRAPHY 

formation. The spectroscope, an instrument for analyzing a substance 
by the kind of light which it emits, reveals not only the mutter of which 
the nebulae are composed, but also that the matter is in rapid motion. 
Calcium, hydrogen, iron, and sodium, the substances of greatest abund- 
ance in the sun, are also among the most abundant substances of the 
earth. 

The Form of the Earth. — The earth is one of the 
planets. From Table I: (Appendix), find how it ranks 
among the other planets in size; — in distance from the sun. 
Like the other planets, it is nearly spherical, but slightly- 
flattened at the poles. It is usually said to be an oblale 
spheroid — that is, a flattened sphere. As it deviates slightly 
from this form, the term geoid is sometimes used to designate 
its irregular shape. 

The spherical form of the earth is shown in various 
ways; it is best demonstrated by surveying a horizontal 
straight line along a level surface, such as that of a pond. 
The line thus projected is not parallel to the surface of the 
pond; the latter curves away from it, and the curvature 
is such as corresponds to the surface of a spherical body. 

This m?y be illustrated in the following manner: Three stakes are 
set in line, or as nearly in line as is practicable, one mile apart, along 
the shore of a canal, a pond, or the sea shore. Sighting marks are then 





EXPERIMENT TO SHOW THE EARTH'S CURVATURE 

made on the stakes each at a uniform distance above water-level. 
An engineer's level is then placed so that the cross-wires cut t he sighting 
marks of the first and third stakes. If the telescope of t he level 1 >e t urnci 1 
upon the middle stake it will be found that the cross-wires cut the stake 
at a point eight inches below the sighting mark. The head and shoulders 



THE EARTH AMONG PLANETS 15 

of a man standing in a boat five miles from shore are visible, but the boat 
itself is not. Among other facts that serve to establish the spherical 
shape of the earth are: The circular shadow of the earth projected upon 
the moon at the time of an eclipse ; the variation of time with respect to 
longitude; and the more practical fact of circumnavigation. 

Were the earth a true sphere, the weight of a body 
would be the same at every part of its surface. This, how- 
ever, is not the case; a given body weighs a little more in 
polar than in equatorial latitudes, and from the difference 
in weight the amount of flattening at the poles has been 
determined. 

A pendulum consisting of a ball weighing about one hundred pounds 
swinging on a wire of fixed length is allowed to oscillate freely. When 
all errors are corrected the rate of vibration will be the same at all.points 
of the earth's surface equally distant from the centre. At any place 
on the earth's surface that is nearer to its centre, as the poles, the rate 
of vibration is slightly faster ; at any place more remote it will be slower. 
The United States Coast and Geodetic Survey has carried on a series 
of pendulum observations covering a period of many years with the 
results as noted below. Professor Ferrel has shown that, theoretically, 
the level of the sea between the 20th and 27th parallels is about thirteen 
metres (40 ft.) higher than it would be if the earth were a true spheroid. 

Size of the Earth. — The following are the earth's 
dimensions : 

Polar diameter 7,901 .5 miles 

Equatorial diameter 7,926.6 miles 

Circumference at equator 24,912.2 miles 

Surface (approximate) 197,000,000 square miles 

What is the difference between the polar and the equa- 
torial diameter? Compare the diameter of the earth with 
that of the sun (Table I., Appendix). Large as the earth 
seems to us, it would require about one and a quarter mil- 
lion bodies of its size to make a globe of the same size as 
the sun. 



16 PHYSICAL GEOGRAPHY 

Motions of the Earth.— Tho earth has several distinct 

motions. It revolves about the sun in an elliptical path, 
making a complete journey of about 585,000,000 miles in 
very nearly 365j days — a period of time called a year. It 
also rotates, or spins on its axis, the time required for a 
complete rotation being called a day. The axis of the 
earth also swings or oscillates in a path which resembles 
that of the peg of a "sleeping" top. 

The revolution of the earth around the sun, together 
with the inclination of the axis, causes the successive change 
of the seasons and the varying length of sunshine and dark- 
ness. Rotation upon its axis causes the succession of day 
and night. The oscillation of the axis causes the precession 
of the equinoxes. 

In long intervals of time it is thought that this motion is connected 
with certain changes of climate. It is a subject, however, that belongs 
to the science of astronomy, and not to physical geography. 

The Inclination of the Axis. — The axis of tho earth 
is not perpendicular to the plane of the earth's path, called 
the plane of the ecliptic, but inclines about 231 degree's, as 
shown in the accompanying figure. The degree of inclina- 
tion varies in long intervals of time, but practically this 
change may be neglected; practically the axis is always 
parallel to itself. The north end of the axis if prolonged 
would extend nearly in the direction of a star named 
Polaris; this star is called the north, or pole star. 

If the earth's axis were perpendicular to the plane of its 
orbit, each place on the earth's surface would have an 
unvarying season. It would be always mild in mid-lati- 
tudes, and equally cold in the same latitudes of polar 
regions. 



THE EARTH AMONG PLANETS 



17 



With an inclined axis, however, the case is different. 
In June (see diagram below) the sun's rays are almost ver- 
tically on mid-latitude parts of the Northern Hemisphere, 
while in the corresponding latitudes of the Southern 
Hemisphere they are very oblique. At this season, there- 
fore, the Northern Hemisphere receives more light and 
more heat than the Southern. Six months later the con- 
ditions are reversed; the vertical rays are oh the Southern 
Hemisphere, while on the Northern they are oblique. In 






INCLINATION OF THE EARTH'S AXIS 

The unshaded hemisphere shows the position of the light circle at each of the Jour seasons. 

December, therefore, the Southern Hemisphere receives its 
greatest warmth. 

Thus each of these hemispheres has a period of warm 
and long summer days, alternating with one of short 
days and cooler temperature. In equatorial latitudes the 
difference is not great, but beyond the tropics it is the 
difference between winter and summer. In polar latitudes 
the sun is shining on the greater part for six months. Each 
hemisphere, therefore, is alternately in light and darkness 



18 



PHYSICAL GEOGRAPHY 



during this period. As a result, the season of sunshine, or 
summer, may become oppressively hot, while the season of 

darkness, or winter, is very cold. 

Any change in the inclination of the earth's axis would produce 
decided changes of climate. For instance, were the inclination increased, 
the limits of the frigid zones would be pushed farther toward the equator. 
If the inclination of the axis were forty degrees, the polar circles would 
each be forty degrees from the poles, and the tropics would be each 
forty degrees from the equator. 

The Effects of Rotation. — The rotation or spinning of 
the earth on its axis causes the succession of daylight and 
darkness. One-half the surface, being always toward the 
sun, is illuminated; the opposite side is in darkness. The 
rotation of the earth presents every part of the surface suc- 
cessively toward the sun, lighting all parts in turn. Were 
the axis of the earth perpendicular to the ecliptic, day and 

night would be of equal 
length at all parts. of the 
earth's surface. On ac- 
count of its inclination, 
the relative length varies, 
not only in different lati- 
tudes, but with the 
changes of the seasons 
in the same latitude. 

In the torrid zone the 
period of daylight and 
darkness does not vary 
much in length, and at 
the equator the days and 
nights are each twelve 
hours long. In the Icin- 




RELATIVE LENGTH OF DAY AND NIGHT 

The shaded part <tj each parallel shows the length 
o) the night; the unshaded part, the proportion- 
ate length oj the day. 



THE EARTH AMONG PLANETS 19 

perate zones the days are longest near the polar circles and 
shortest near the tropics, varying from thirteen to twenty- 
four hours. Within the frigid zones day and night cor- 
respond practically to summer and winter. There, both 
the day and the night vary from a few moments to six 
months in length. 

The relative length of daylight and darkness and the 
changes of the seasons have much to do with food crops. 
The long days and short nights of summer in the tem- 
perate zones make possible the cultivation of plants that 
would not mature were the day only twelve hours in 
length. 

Only a few species of animals and plants thrive in regions 
of long-continued darkness, and the}' are mainly the lower 
forms; the higher species require an environment in which 
light and darkness follow one after the other in periods of 
short duration. Most plants fail to mature and fructify 
unless exposed to strong light, and many species will not 
live at all. 

QUESTIONS AND EXERCISES. — Make a circle one inch in diam- 
eter on the blackboard, and from the centre of this circle, with a 
radius fifty-five inches long, draw as much of the arc of a circle as the 
size of the blackboard will permit. The two circles represent the 
relative size of the earth and the sun. 

In the diagram, p. 17, the axis of the earth is inclined 23*° from 
the dotted line; which of these positions represents summer in 
the Northern Hemisphere? — In the Southern? Copy the diagram, 
p. 18, and mark the point the sun's rays reach beyond the north 
pole; how many degrees from the pole to this point? What circle 
passes through this point? Mark the point on the circumference 
where the rays are vertical. What circle passes through this point? 
From each pole to the equator the angular distance is 90 : find the 
distance in degrees from the Arctic Circle to the Tropic of Cancer; 
this distance is the width of the Temperate Zone. If the inclination 
of axis were 28 , what would be the width of each light-zone? If 



20 PHYSICAL GEOGRAPHY 

32 ? Ninety degrees less twice the angle of inclination equals the 
width of the Temperate Zone. 

From the datum given on p. 15, calculate the speed of the earth 
per second at the equator; compare this with the speed of a train 
scheduled at sixty miles per hour. With reference to the earth's 
rotation on its axis, what is the speed per hour of a point on the 
equator? In latitude 6o° it is about half as great; how great is it 
at the poles? 

In the diagram, p. 18, the proportionate length of the longest day 
and shortest night are shown by the shading; determine by measure- 
ment the length of the longest day in latitude 40 ; in latitude 6o°. 
Subdivide the parallel into twenty-four parts by halving it three times 
and dividing the last subdivisions each into three parts; each of the 
smallest subdivisions has practically an hour value. 

COLLATERAL READING AND REFERENCE 

Mill. — Realm of Nature, pp. 63-81. 
Redway — Manual of Geography, pp. 64-78. 
Howe. — Elements of Astronomy. Problems, a-g, p. 83. 
Jackson. — -Astronomical Geography. 
Todd. — New Astronomy, chaps, v-vi. 
Newcomb. — Popular Astronomy, pp. 88, 397. 

Museum op Natural History, New York City. — Collection of me- 
teorites, photographs of planets, nebula? and other celestial bodies. 



CHAPTER II 

THE STRUCTURE OF THE EARTH 

In the long period of time that has elapsed since the 
earth was glowing with intense heat, the substances com- 
posing it seem to have adjusted themselves in accordance 
with the laws of gravitation — that is, the heaviest kinds of 




IDEAL SECTION THROUGH THE EARTH 

The thickness of the various envelopes is greatly distorted. 

matter are nearest the centre. Structurally the earth con- 
sists of a dense and practically solid globe, the lithosphere, 
nearly covered with a comparatively thin layer of water, 

21 



22 PHYSICAL GEOGRAPHY 

the hydrosphere, the whole being surrounded by an envelope 
of air, or atmosphere. 

The shape of the lithosphere and the condition of the 
substances composing it, show that in times past it was 
intensely heated, and that much of the rock composing 
it has been in a molten condition. The globular form is 
the only one that would naturally result from the action of 
gravitation on a plastic or a fluid body; and the flattening 
at the poles is most reasonably explained by a hypothesis 
that, while it was still plastic, the earth spun, or rotated 
on its axis. 

The density of the lithosphere, together with the waters, 
is about that of iron ore — that is, bulk for bulk, it is about 
five and one-half times as heavy as water. At the surface, 
however, the density of the rocks is about half as great 
as that of the whole globe; it is certain, therefore, that 
the substances forming the interior are much heavier than 
those at the surface. 

The outer part of the lithosphere, called the rock envelope 
or, popularly, the "crust of the earth," surrounds an in- 
tensely heated interior, the centrosphere. 

That the centrosphere is very hot cannot be doubted; 
for in every place where the rock envelope has been pene- 
trated by deep borings, a constant increase of temperature 
is observed — the greater the depth the higher the tempera- 
ture. The thickness of the rock envelope is not known, but 
at a depth of less than forty miles it is thought that the 
temperature is high enough to fuse the most refractory 
substances. 

It must not be inferred from this, however, that the centrosphere 
is liquid; on the contrary, the earth behaves like a solid hut somewhat 
elastic body. The melting or fusing of a substance depends not alone 



THE STRUCTURE OF THE EARTH 23 

on temperature, but also on pressure. With increase of pressure, the 
fusing point is also raised; and the great weight of the overlying rock 
produces pressure enough to prevent liquefaction. The increase of 
temperature varies in different kinds of rock and in different localities, 
the average being one degree (F.) for every sixty or seventy feet. 

Four-fifths of the surface of the rock envelope is covered 
by a layer of water, the hydrosphere, averaging a little 
more than two miles in depth. The water not only exists 
in a free state, at the surface, but also as a chemical con- 
stituent of various kinds of rock. 

The crystalline form of many rocks is due to the water they contain 
in chemical combination, and there are but few rocks of which water 
does not form a considerable part. It is by no means impossible that 
the free waters of the earth, in time, may be absorbed in this way, to 
reappear in chemical combination. 

Water forms a most important constituent of the earth. 
It is essential to the existence of life; for not only does it 
form the greater part of every plant or animal, but it is also 
the chief means by which nutrition is distributed through- 
out the various parts of the body of the animal or the plant. 

Within a range of a very few degrees of temperature, 
water exists in one or another of three forms — a solid, ice; 
a liquid, water; and a vapor, steam. In one or the other 
of its forms water is the chief agent by which the surface of 
the rock envelope has been sculptured; therefore it has an 
important place in the science of physiography. 

The Atmosphere. — The atmosphere consists of a mixt- 
ure of gaseous substances, namely — nitrogen, oxygen, 
water vapor, and carbon dioxide. Oxygen is required in 
the respiration of animals; carbon dioxide, the gas formed 
when coal burns, is essential in the breathing of plants; 
nitrogen forms a part of the structure in both animals and 



24 PHYSICAL GEOGRAPHY 

plants; and water vapor is the form in which the fresh 
water is carried from the sea to the land. The atmosphere, 
therefore, is just as essential to life as the water envelope. 

The thickness of the atmospheric envelope is not known. 
Various estimates place it between one hundred and two 
hundred miles. At the latter estimate, on a globe three feet 
in diameter, the proportionate depth of the atmosphere 
would be about one-half an inch. 

At the plane where the atmosphere rests upon the land 
and the sea the physiographic processes which are most 
noticeable are continually in action. 

The Rock Mantle. — The three envelopes of the earth 
are constantly acting and reacting upon each other. Move- 
ments of the rock envelope have divided the waters from 
the land. Moreover, the rock envelope has been crumpled, 
and folded so as to form plateaus, ranges, and valleys. 
The heat of the sun causes a part of the ocean waters to 
take the form of vapor, and the latter, mingled with the 
air, flows over the land. Being chilled, the vapor again 
takes the form of rain or of snow, and falling on the land 
wears away its surface. The water, gathering into channels, 
carries the particles of rock waste mingled in its flood to 
the sea, and there deposits them. 

As a result, almost every part of the rock envelope is 
covered with a layer of loose rock that has been worn from 
its surface. This layer is called the rock mantle, or some- 
times the waste mantle. It is usually thick in the valleys 
and along the coasts to which it has been carried by run- 
ning water; it is apt to be thin, or absent altogether on 
mountain slopes. The rock mantle is composed of about 
every mineral substance that enters into the structure of the 
rock envelope. The top of the rock mantle is commonly 



THE STRUCTURE OF THE EARTH 25 

mixed with the remains of decayed vegetation. It contains 
the elements of plant food and constitutes soil. 

For convenience, the constituents of the rock mantle are classified 
as follows: Clay, a silicate of the metal aluminium, is derived from 
the mineral felspar. Sand consists of grains of uniform size derived 
from the mineral quartz. As a rule, sand is a seashore product, and the 
uniform size of the grains results from the sorting power of the waves. 
Sand is also formed by the action of the wind. The name is applied 
loosely to any deposit of finely sorted grains of rock. Gravel is a 
term loosely applied to any accumulation of small pieces of rock. For 
the greater part, gravels are found along stream beds, in glacial drift 
and on shores. Peat is a black, slimy muck, composed mainly of carbon, 
that results from the decay of vegetable matter. It occurs chiefly 
in swamps, and old lake bottoms. The name is also applied to the 
stems of certain swamp plants. Marl is a limy substance, usually 
mixed with clay, that results from the decay of minute living organisms, 
shell-fish, etc. It is valuable as a fertilizer. The rock mantle consists 
chiefly of a mixture of sand, clay, and the products of decayed vegetation. 

Movements of the Rock Envelope. — The most ap- 
parent changes in the surface of the rock envelope are the 
wearing away of the' rock from the higher surfaces and the 
transportation of the rock waste to lower levels. That is, 
water in its various forms loosens particles of rock, and the 
streams carry it seaward. If the land were everywhere 
level, the run-off of water could wear away but little of it. 
But vertical movements of the rock envelope are taking 
place, and these, by making new slopes, give the run-off 
waters increased wearing power. 

These never-ceasing changes make a fairly complete 
cycle. Thus, vertical movements of the rock envelope 
form mountains and plateaus. By the action of water in 
its various forms, these are gradually worn down, and the 
rock waste that once composed them is transported to the 
shores of the continents and there spread out in the form 



26 PHYSICAL GEOGRAPHY 

of a long margin of sediment. The sediments, in turn, 
become layers of rock; in time these are folded into mountain 
ranges or uplifted in the form of plains and plateaus. 
Practically every part of the earth's surface has undergone 
changes of this sort. 

In areas to which extensive sediments are being carried, 
evidence of sinking is usually apparent; while, as a rule, 
areas that arc being denuded are rising. It is probable, 
therefore, that vertical movements of the rock envelope 
in many instances are connected with the wasting of the 
land and the transfer of sediment. 

The causes of these earth movements are not known, but it is be- 
lieved that the gradual contraction of the rock envelope to fit itself 
around a more rapidly shrinking interior is the chief factor. There 
is evidence, too, that gravitation is a factor. The removal of great 
amounts of rock waste — from one locality to another, relieves weight 
at one place and increases it at the other. Therefore it is inferred 
that a sinking occurs at the latter place, and an uplift at the former. 

According to this principle the rock envelope of the earth always 
maintains a state of balance, adjusting itself to the load it carries. 
This condition, called the isostatic balance, is regarded as an important 
factor in the explanation of the various movements of the rock 
envelope. 

In general the vertical movements of the rock envelope 
are of two kinds: the uplift, folding, crumpling, and break- 
ing which may be observed in the formation of mountain 
ranges; and the gentler movements observed in the slight 
uplift or the depression of areas of considerable size. 
Between the two kinds there is no broad distinction. 
Usually such movements are slow, covering periods of many 
centuries in duration. Occasionally, however, it takes the 
form of a sudden break of the rock envelope, thereby pro- 
ducing an earthquake. 



THE STRUCTURE OF THE EARTH 27 

Rock and its Structure. — The term rock is applied to 
every mineral substance that forms a part of the earth, and 
likewise to any mixture or combination of minerals. Thus, 
clay, sand, gravel, limestone, quartz, granite, lava, and 
even the fine, wind-blown rock waste, are each called rock. 
Beyond a depth of a few thousand feet from the surface, 
nothing positive is known about the character of the sub- 
stances which compose the earth. Nothing at all is known 
about the centrosphere, and but little is known about the 
lower part of the rock envelope. 

No one knows what the primitive or first rock that formed 
the crust of the earth may have been, but certain kinds of 
rock have been found underlying the water-formed sedi- 
ments, from which the latter seem to be derived. Ordinary 
granite is an example of this kind of rock, and granitic 
rocks are very abundant. There are various kinds of 
granite, but the most common varieties contain the min- 
erals of which nearly all the elementary rocks are com- 
posed. 

One of these minerals is silica, of which quartz and sea 
sand are the best examples. Another is felspar, a mineral 
which, decomposed, yields clay, potash, lime, and soda. 
Another mineral is hornblende, which decomposes mainly 
into iron, lime, and silica. Still another constituent usually 
present is mica, popularly called "isinglass"; like felspar 
mica also decomposes into clay, silica, lime, and other 
substances. 

Igneous Rocks. — In many instances there is no doubt 
how the rock has been formed, or whether it has been al- 
tered, because the whole process of its formation has been 
carried on in plain sight. Thus, when a volcano pours out 
a flood of molten lava there is no question about how the 



28 



PHYSICAL GEOGRAPHY 



rock got into place, or whence it came. When it lias 
hardened, the lava always has qualities about it that deter- 
mine its character. 

Of the rocks that have cooled from a molten condition, 
the lavas of volcanoes are perhaps the best known. The 
Hawaiian Islands are mainly great piles or domes of lava. 
Lava is common in most mountainous regions. In many 




IGNEOUS ROCK: A FLOW OF LAVA 

instances it has been ejected from long fissures and has 
cooled slowly, forming great dykes; in this form it is usually 
known as basalt, or, if it breaks into regular blocks, trap. 
The Palisades of the Hudson, Fingal's Cave, and the Giant's 
Causeway are examples. 

All the foregoing are commonly called vulcanic or igne- 
ous rocks. Igneous rocks are found not only in mountain- 
ous regions, but also in localities from which the sedi- 
mentary rock has been removed. Granitic rocks prevail in 



THE STRUCTURE OF THE EARTH 



29 



the New England Plateau; dykes and sheets of lava are 
abundant in the Western Highlands. 

Normally, granite is a mixture of mica, felspar, and quartz. If it 
contains hornblende instead of mica it is called syenite; if both mica 
and hornblende are present it is syenitic granite. If the felspar contains 
soda the granite is diorite. If it occurs in layers, it is called gneiss. 




SEDIMENTARY ROCK, NEAR OLEAN, N. Y. 
The jace oj the cliff is one side oj a channel of the river. 

Sedimentary Rocks. — Most of the rock now at the sur- 
face consists of sediments carried thither by running water 
and deposited in the form of layers, or strata, that afterward 
hardened into compact rock. Moreover, there is but one 
place from which the sediments could be derived — namely, 
from the rock envelope itself. 



30 PHYSICAL GEOQRAPHY 

Although the sedimentary rocks are derived from granitic 
and other vulcanic rocks, there is nothing to indicate their 
close relation to them. The making of firm rock out of 
loose sediments is sometimes a complex process, as may be 
seen in the formation of sandstone. 

In the first place the grains of quartz composing the 
sandstone are rounded; they also are uniform in size. The 
rock from which they came, probably granite, has crumbled, 
and water has sorted the various minerals from one another. 
The waves, beating the fragments of quartz and rubbing 
them against one another, have not only separated them 
from the rest of the granite, and rounded the grains; they 
have also sorted them according to size, and piled them in 
nearly flat layers along the beach. 

In time the beach was lifted above sea-level and cov- 
ered deep with loam. Water, in one form or another, 
flowed over upon the surface; the lime it contained in 
solution, leached through the layer of sand, and cemented 
the grains, forming sandstone. In a similar way, water con- 
taining lime, or perhaps iron, in solution has cemented 
gravel into conglomerate, breccia, "pudding stone," or 
" brown stone." 

In most instances, clay banks are derived from granitic 
and similar rocks. Felspar decomposes into clay, and the 
latter, being very light and fine, is carried off by the water, 
to settle by itself. In many instances clay has been spread 
over large areas. Possibly it remained in the stiff, pasty 
form by which it is commonly known; very likely pressure, 
heat, and moisture, acting together, converted it into shale 
or into slate. 

An interesting example of rock-format ion occurs at Sweyney Cliffs, 
Shropshire, England. A small stream of water pours over :i red sand- 



THE STRUCTURE OF THE EARTH 31 

stone cliff. The water contains a considerable proportion of lime and 
magnesia; and a species of coarse moss grows freely in the saturated 
earth about the stream-bed. The mineral salts of the water are deposited 
copiously on the moss, and little by little the latter, together with the 
other matter entangled, has become completely incrusted and forms a 
dyke about twenty feet wide. The dyke has built itself out from the 
edge of the cliff a distance of ten feet or more. 

Rivers and other running waters are active workers in 
making rock, and one can almost always find clay banks, 
gravel beds, and other sediments that have been brought 
down stream and distributed by the current. 

It is not so easy to understand how rocks are found at 
the bottom of the sea; as a matter of fact, more sedimentary 
rock has been formed in ocean and lake beds than else- 
where. Many of these rocks are composed largely of the 
remains of minute animals. 

The sea, especially in regions of warm water, contains 
many thousand species of such animals, all of which 
multiply with great rapidity. When they die their bodies 
sink to the bottom. The mineral remains of these organisms 
consist mainly of lime or silica, and in time the thick layer 
that accumulates finally becomes cemented into rock. The 
growth of such rock is slow, but time alone is required to 
make layers of great thickness. The chalk cliffs of England 
and France were formed in this manner, and they aggregate 
nearly half a mile in thickness. The limestones of the 
Mississippi Valley also accumulated on sea-bottoms and 
have about the same thickness. 

There are very many forms of sedimentary rock, though only a few 
kinds. Thus, the limestone that gathers about springs is called tufa 
when soft and porous; or travertine when white, hard, and partly 
crystalline. If it is composed of small, rounded grains, it is oolitic, or 
"bird's-eye" limestone. Shale takes many forms; and clay, though 



32 PHYSICAL GEOGRAPHY 

white when pure, is usually gray, or reddish-brown. If it contains a 
considerable proportion of vegetable matter, it is black "adobe." 

Metamorphic Rocks. — In many instances the character 
of sedimentary rocks has been materially changed. Thus, 
by pressure and heat, moist beds of clay have been trans- 
formed into layers of gritty sZafe;chalk and limestone have 
become crystalline marble: shales have been converted to 
mica schist; and bituminous coal has become anthracite. 
Older granitic rock has crumbled, and the rock waste has 
been cemented into firm rock again with but little altera- 
tion, as in the case of certain kinds of gneiss. Such rocks 
are said to be metamorphic. 

Substances ordinarily insoluble in water are quickly changed when 
subjected to water under a high temperature. If a thick steel tube, 
filled with water and fragments of granite, be intensely heated for 
several hours, the larger part of the rock will be dissolved. Hot al- 
kaline water also dissolves granitic rocks, the dissolved matter being 
precipitated when the water cools. 

In most cases the older and deeper stratified rocks have 
been thus changed. The weight of the overlying rock 
produces immense pressure, and the changes resulting from 
the moisture within them greatly alter their appearance. 
Many of the metamorphic rocks, indeed, are like igneous 
rock in appearance. Rocks that form a part of mountain 
folds are apt to be metamorphic on account of the pressure 
that has resulted from the folding and crumpling. 

Order of the Rock Strata. — Most of the sedimentary 
rocks were deposited in horizontal layers, but, on account 
of the movements of the rock envelope, they are often 
found in oblique positions. Sometimes they occur in 
gentle folds; but in mountainous regions they are much 
crumpled and broken. In some of the old sea-beds now 
raised above sea-level the strata are undisturbed. 



THE STRUCTURE OF THE EARTH 



33 



The story of the earth has been read by the study of 
the upturned edges of broken and tilted strata. Each 
stratum is a chapter by itself; and to read the history prop- 




SEDIMENTARY ROCK: SECTION THROUGH THE CANON OF THE COLO- 
RADO RIVER 

The level o] the strata has not been disturbed. 

erly it is best to begin with the lowest. It is not always 
easy to tell the relative position of strata at some distance 
from one another, but as each stratum has fossils, or ani- 
mal remains peculiar to itself, the position is usually de- 
termined by the character of these. 

The total thickness of the stratified rocks is not far from 
twenty miles; the average thickness is, perhaps, between 
five and ten miles. There is no locality in which all the 
various strata are found ; no locality is known in which even 




SEDIMENTARY ROCK: TILTED STRATA 

any considerable number occur. Sometimes the oldest 
rocks are overlaid by the most recent formations; the inter- 
mediate strata are missing. 

Thus, the rocks of the Mississippi basin belong to a very old and 
remote geological period. A thin cover of rock waste that belongs 
chiefly to a very recent period overlays them. 

As a rule, the lowest strata do not differ much from the 
granitic rocks and possibly include some of them. To these 



34 



PHYSICAL GEOGRAPHY 



the name Archrcan is given. These strata are regarded as 
the foundation of the continents and the floor of the oceans. 
The decay and wearing away of these has formed the 

material of which nearly all the 
sedimentary rock, the limestones 
excepted, is composed. "The 
waste of the old (and is the ma- 
terial of the new." 

The remaining strata are 
named in accordance with the 
character of the life fori i is that 
existed when the rocks were un- 
dergoing formation. Note the 
eras in the order of their occur- 
rence. 





UNCONFORMABLE STRATA: 

CANON OF THE COLORADO 

RIVER 

The tilled strata, originally horizontal, 
■were deposited on the surface oj the 
igneous rock. Subseqtiently the upper 
layers were deposited on the broken sur- 
face oj the tilted layers. 

land ; Huronian, from "Huron" 
All these names are derived from 
first studied. 



The word A rchcean means "the be- 
ginning"; Palaeozoic is derived from 
two Greek words meaning "early life " ; 
Mesozoic, similarly, is "middle life"; 
and Cenozoic, " recent life." The Silur- 
ian age was named from "Silures," a 
former name for the people of Wales; 
Devonian comes from " Devon," Eng- 
; and Laurentian from " St. Lawrence." 
the localities in which the rocks were 



The Archaean Era.— In Archaean times North America 
consisted mainly of a narrow, V-shaped strip of land south 
of Hudson Bay. The crests of the Appalachian Mountains 
were just above the sea-level; the Black Hills and one or 
two peaks of the Rocky Mountains had also just emerged. 
The general form of the American continent was outlined 
in Archrcan times. With the possible exception of a few 



THE STRUCTURE OF THE EARTH 



35 



species resembling the 
sponge, no forms of 
life are found in Arch- 
aean rocks. 

The Palaeozoic 
Era. — The Palaeozoic 
era was of very long 
duration. The sedi- 
ments composing it 
are in places 25,000 
feet thick. The 
greater part of Eu- 
rope and North Amer- 
ica were above sea- 
level during this 
period, but the land 
was many times up- 
heaved and sub- 
merged. In North 
America the greater 
part of the Mississippi 
Valley was a shallow 
inland sea, that later 
became an immense 
marsh. 

In the variety and 
extent of life forms 
the Palaeozoic era is 
the most noteworthy 
of all the geological 
periods. It began 
with the lowest form 




ORDER OF STRATA 



36 



PHYSICAL GEOGRAPHY 



of sponges and closed with the advent of mammoth rep- 
tiles. During this period animals with backbones appeared 
for the first time. Insects were numerous, and toward the 
close reptiles existed. Fishes and mollusks seem to have 
been the prevailing forms. 

The climate was warm and moist. The vast accumula- 
tions of vegetable matter that now constitute the coal fields 
were found in swamps of this era. In North America 
these swamps covered much of the area that is now the 
central United States. 

Coal measures are not confined to the Carboniferous age; they occur 
in all geological ages. Those of the Carboniferous age, however, supply 
nearly all the coal consumed in the United States. The coal measures 
of the Pacific coast belong to the Tertiary age. 



The Mesozoic 




NORTH AMERICA IN ARCH/EAN TIMES 

The shaded area shows the pari oj the continent 
above sea-level. 



Era.— During the Mesozoic era both 
North America and Eu- 
rope had about reached 
their present shape. In 
the former continent the 
Gulf of Mexico reached as 
far north as the mouth of 
the Ohio, and a north- 
western branch of it ex- 
tended nearly to Canada. 
In Europe the higher 
elevations of land, the 
Pyrenees excepted, had 
probably been eleva bed 
above sea-level. 

It was an age of gigan- 
tic reptiles. The animals 
of some species were 



THE STRUCTURE OF THE EARTH 



37 



from sixty to eighty feet in length. For the first time 
birds appeared. They were very much like reptiles, how- 
ever, and some species had jaws with socket teeth, instead 
of horny beaks. 

The Cenozoic Era. — This era was largely one of uplift 
and mountain-making, al- 
though both in North 
America and Europe the 
various ranges and sys- 
tems had received defi- 
nite forms. The former 
was a continent of vast 
fresh-water lakes; the lat- 
ter of inland seas. 

Many of the life forms 
which had flourished in 
preceding ages were com- 
mon, but one great step 
in advance may be noted 
— the first appearance of 
mammals. These i n - 
eluded the elephant, 
camel, rhinoceros, wolf, deer, and horse. The forest trees 
both of North America and Europe included most of the 
species found to-day. 

There were several species of camel during these times. It is interest- 
ing to note that this animal, now confined to the Asian continent, was 
a native of the American. The earliest species of horse had five toes 
instead of one. In subsequent times two of these gradually disappeared. 
The horse of modern geological times has but one toe, but the " splint 
bones" just above the hoof are the toes of the Quaternary horse. 




NORTH AMERICA IN CENOZOIC TIMES 

The unshaded area shows the part oj the continent 
above sea-level. 



The Glacial Epoch. — The close of the Cenozoic era was 



38 



PHYSICAL GEOGRAPHY 



very abrupt, It was probably duo to an eleval ion of a large 
part of North America and Europe from 1,000 to 2,000 
feet, and was accompanied by a decided lowering of tem- 
perature. The ice and snow of the north polar regions 
crept southward until they enveloped nearly all of Europe. 
In North America the ice reached as far south as the Ohio 
and Missouri Rivers. This prevalence of ice constituted 
the glacial epoch. It is marked by a scattering of drift on 
a stupendous scale similar to that which marks the glaciers 
of the present time. 

In the area covered by glacial ice most of the species of 




THE UNITED STATES AT THE BEGINNING OF THE QUATERNARY AGE 
The shaded area shows the pari added in recent limes. 



larger mammals perished. The cave bear, horse, wolf, and 
reindeer survived. Many species of plants were destroyed. 
It seems certain that man existed before the close of the 
glacial epoch. In the caverns of Belgium, Germany, and 
Italy the bones of man have been found in caves together 
with the skeletons of animals and various implements of 
the chase. From the few scraps of unwritten history it 
seems that preglacial man was a savage of the lowest type. 



THE STRUCTURE OF THE EARTH 39 

He lived in caves and obtained his food by hunting and 
fishing. He did not cultivate the soil nor did he have any 
domestic animals. He had learned -the use of fire, how- 
ever, and from that moment his intellectual development 
was rapid. 

QUESTIONS AND EXERCISES. — It is sometimes assumed that 
the rock envelope is about forty miles, and the atmosphere about 
two hundred miles, in thickness. Construct a diagram on the black- 
board or on paper, showing the relative thickness of each on scale 
in the ratio of 4000 : 40 : 200. 

Unburnt clay can be moulded and shaped when wet; is this true 
of burnt clay? " Burning," or heating clay drives off the water 
of crystallization, leaving a hard mass. What great industries de- 
pend upon this fact? Examine grains of sea sand under a magnifying 
glass, and note their characteristics. Compare them with the loose 
dust in the streets. Compare stream gravel with ordinary broken 
rock, and note the difference. 

Note and describe any instances within your personal knowledge of 
the action of water on the rock envelope; explain the nature of the 
changes and how they have been brought about. 

Study the various rock formations in the neighborhood in which 
you live and classify them according to their origin — that is, as sedi- 
mentary, metamorphic, or igneous. 

Make a collection of them for future use. 

A stream flows over a bed of limestone rock that is slightly 
soluble, into a lake without an outlet; what changes in the formation 
of rock are likely to occur? Will the rock formed be stratified or 
unstratified? In what way may it become fossiliferous? 

From the official State reports, or from the United States Geological 
Survey, find the order and distribution of rock strata in the State 
in which you live, and from the information given construct a geologi- 
cal map. 

Procure one or more specimens of granite, and with the aid of a 
magnifying glass observe the following directions. Look for small 
clusters of foliated or "leafy" mineral; it may be whitish or, per- 
haps, green, or brown; this mineral is mica.. If no mica is found, 
look for jet black crystals or masses ; this is hornblende ; it is 
usually opaque, but sometimes translucent. Find the white, trans- 
lucent mineral with, glassy lustre ; it is quartz, or silica, and it is apt 



40 PHYSICAL GEOGRAPHY 

to form the chief bulk of the rock. Look also for an opaque mineral 
varying from yellowish-white to pink in color ; possibly it will break 
into fragments having flat sides, or clea.<va.ge planes ; this mineral is 
felspar ; it has different crystalline forms accordingly as it contains 
lime, potash, or soda. Study the character and appearance of 
trap, basalt, and obsidian ("volcanic glass"), if possible. 

Procure pieces of limestone of various kinds, including chalk 
(not crayon), specimens of clay and shale, and one or more kinds 
of sandstone. Touch the limestone with a drop of strong acid 
held on the end of a glass rod ; note the result. If possible collect 
some of the escaping gas in a bottle and put a lighted match into 
it; note the result. The gas is carbon dioxide. Shake a lump of 
clay vigorously in a bottle partly filled with water and note whether 
the sediment falls quickly to the bottom, or remains suspended. 
Try the same experiment with sand. In how many directions does 
the shale split or break? 

Obtain specimens of iron ore, marble, and dry clay, and compare 
the weight of pieces of the same size. If possible find the specific 
gravity of each. Determine, or judge by " hefting," the relative 
weight of the various kinds of rock in the neighborhood in which 
you live. 

Procure specimens of clay and slate, chalk (not crayon) and 
marble, bituminous (soft) coal and anthracite. Examine each pair 
with reference to hardness, foliation, crystalline appearance, and 
density (weight of pieces of equal size). Make a list of the rocks 
occurring in the neighborhood in which you live, and classify them 
as igneous, sedimentary, or metamorphic. 

COLLATERAL READING 

Powell. — Physiography of the United States, pp. 22-29. 
Le Conte. — Elements of Geology, pp. 127-132. 
Mill.— Realm of Nature, pp. 211-230, 249-2G1. 
Shaler. — First Book of Geology, pp. 107-124. 



CHAPTER II f 



LAND AND WATER, AND THEIR OUTLINES 

The surface of the rock envelope is not smooth, nor is 
any considerable part of it perfectly level, as the word is 
commonly used. More than three-fourths of its surface is 
covered by the sea, but the remaining part consists of very 

irregular areas that arc 
higher than the level of 
the water. The great 
body of water that cov- 
ers so much of the rock 
envelope is the sea: the 
areas above sea-level 
constitute the land. The 
lowest part of the rock 
envelope below sea-level 
— that is, the lowest part 
of the sea-bottom — is about five and one-half miles, and 
the highest point above it is just about the same distance. 
The average elevation of the land is not far from 2,000 feet, 
but the average depth of the sea is about 2,000 fathoms. 

The land aggregates about 53,000,000 square miles. It 
clusters around the north pole, and from this circumpolar 
region it radiates toward (ape Horn, toward the (ape 
of Good Hope, and toward Tasmania. In which hemi- 
sphere is the greater part? Which of the two temperate 
zones includes the greater area? The two largest masses 

42 



OCEANIC AREA 




COMTI NE NT^L 
A R EA 












□ 






ISLANDS 





RELATIVE AREAS OF LAND AND WATER 



LAND AND WATER 



43 



are nearly divided at the central part. The smallest is 
separated by an arm of the sea which seems to have severed 
it from the largest. The three largest land masses are called 
continents; the smaller ones islands. The line at which the 
land and the sea meet is the shore; the narrow strip of land 
next the shore, the coast. 

The notable separation of the land masses has been aptly called the 
"zone of fracture." The isthmus of Panama is scarcely thirty miles 
wide and the isthmus of Suez is only one hundred miles across. Yet 
these two necks of land are all that connect the divisions of each con- 
tinent. Twenty-five thousand miles of open navigation are obstructed 
by a width less than one hundred and thirty miles of land. Even 
these commercial barriers are disappearing because of canals completed 
or projected. 

The Continents. — The continents are so called on ac- 
count of certain features of their structure. Each one, for 



< 








hi 

n. 












z 
< 


SOUTk 
AMERICA. 


NORTH 
AMERICA 


AF RICA 




a. E 


u 


R 


A 


S 


A 













D 













RELATIVE AREAS OF THE CONTINENTS AND GRAND DIVISIONS 

convenience, is divided into grand divisions. In general, the 
continents have a high border on one side and a lower one 
on the opposite side. They are variously named, but they 
are usually styled the Eastern, or Asian; the Western, or 
American; and the Australian. The shore of a continental 
body of land in the south circumpolar regions is known 
to exist, but very little is known of its extent. 

It is now the custom to restrict the term "continent" to the largest 
land masses, but it is sometimes more convenient to apply it to a grand 



0° Longitude 90° East from 120° Greenwich 150° 




n 



»F THE AVORLD 

showing 
GHT OF LAND 

and 
TH OF WATER 



to 3,000' 
3,000' to 12,000' 
12,000' to 18,000 
over 18,000' 



ANTARi. 
OCEA 



TIC 

N 



30" 



Longitude 80° East from 120° Greenwich 150° 



46 PHYSICAL GEOGRAPHY 

division. Europe and Asia are also called continents, but the real 
boundary between them is the desert highland that separates western 
from oriental civilization. Physically it is better to treat Eurasia as 
a whole. Politically and historically the two divisions are best con- 
sidered separately. That part of Africa north of the Sahara historically 
is a part of Europe; the unity of history involves the whole of the Medi- 
terranean basin, and not a part of it. 

The entire extent of the continent is not apparent; in 
many places each one comprises an area somewhat greater 
than the part above water, being surrounded by a margin 
which varies from a few rods to one hundred miles or more 
in width. Upon this margin the sea is comparatively 
shallow; beyond it the surface slopes abruptly into deep 
water. 

The submerged margin is very properly considered a 
part of the continent. The depth of water along its extent 
varies, and in places the margin itself reaches above sea- 
level. This margin, which is more or less continuous, forms 
a high surface in comparison with the surrounding sea- 
bottom. It is usually called the continental shelj : ; or con- 
tinental plateau. The map, pp. 44^45, shows both the high- 
land and the lowland regions of each continent and also its 
submerged shelf. • 

The highlands are represented by the area above the 
level of 2,000 feet: compare the extent of highlands and low- 
lands in each continent. Each highland is a great plateau 
rimmed by lofty mountains. About one-fifth of the Ausl ra- 
ttan, two-fifths .of the American, and three-fifths of the 
Asian continent are above the 2,000-foot contour. If we 
consider the land surface as a whole, a little more than one- 
fourth is below the contour, or level, of six hundred feet : 
three-fourths are below the contour of 3,000 feet. 

Elevation of the Land. —There is a great difference in 



LAND AND WATER 47 

the altitude of the high regions of the continents. The 
great plateaus of North America are from one to one and 
a half miles above sea-level; those of South America, about 
two miles; and the highest parts of Asia are more than three 
miles above sea-level. The mountains that rim the high- 
lands in many instances are about twice as high. 

The slopes toward the Arctic and Atlantic Oceans are 
long and gentle; how does this fact compare with the 
slopes of the Pacific and Indian Oceans? As a rule, the 
lowland regions are more nearly level than the highlands. 
On which side of the eastern continent are its principal 
lowlands? On which side of the American continent are 
they situated? 

The mean elevation of the continents varies considerably. 
If their surfaces were levelled off Australia and Europe 
would be not far from one thousand feet high; North 
America and Africa about two thousand feet; and Asia 
nearly three thousand feet. Africa would be probably a 
little higher, and South America not quite so high as 
North America. If all the land above sea-level were 
thrown into the Atlantic Ocean it would not fill the latter. 

In a few localities there are depressions below sea-level. 
The surface of the Caspian Sea is eighty-four feet below 
that of the Mediterranean ; the Dead Sea, situated in a gash 
north of the Red Sea, is thirteen hundred feet below sea- 
level. There are. two small depressions in North America, 
north of the Gulf of California; and several in Africa, south 
of the Atlas Mountains. These were former arms of the 
sea which were severed from the main body. 

Islands. — The islands have an aggregate area of about 
three million square miles, or about one-seventeenth of the 
entire land surface of the earth. Most of them are situated 



48 



PHYSICAL GEOGRAPHY 










3£ii 



on the continental plateau, and are at no great distance 
from the continents to which they belong. Some are the 
higher summits of partly submerged mountain ranges. 

They are parallel to the 
maritime ranges of the 
continent, or possibly, 
they extend from it. Find 
two such chains near the 
American continent, two 
near the Asian continent. 
Islands of this character 
are usually called conti- 
nental islands; and the 
reason is obvious. 

Here and there are is- 
lands in mid-ocean, far 
distant from any large 
body of land. They arc 
called oceanic islands. 
a stretch of the coast of Norway There i s n o d o u b t 

The coast, deeply indented with fjords, is bordered r ii • • r 

by many thousand rocky islets. regarding the Ol'lglll 01 

some of them; they con- 
sist of the lava that has been ejected from volcanoes. In 
some instances these islands are solitary, as Jan Mayen 
and St. Helena; in others they form a chain, as the 
Hawaiian group. 

The numerous islands in the Pacific Ocean form the grand 
division Polynesia. These islands occur in regular chains 
that are roughly parallel; they are the higher summits of 
submerged mountain-ranges. In some instances a vol- 
canic peak is in sight, but in others the position of each 
peak is marked by the reef of coral growth that encir- 




LAND AND WATER 



49 



cles it. The islands themselves are popularly known as 
coral islands. 

The coral polyps, of whose mineral remains these islands and reefs 
are formed, are an animal growth not unlike a tree with its branches. 
The mouths of the polyp completely cover its upper surface somewhat 
as the flowers of the hollyhock or mullein cluster about the stem. In 
a single community the growth of the polyp is chiefly upward, but where 
the communities are thickly clustered, their branches interlock and 
finally form a compact mass. The living portion of the coral reef is 
at the surface of the water or a few feet below it; the dead parts may 
extend a hundred fathoms or more below the surface. 




AN ATOLL, ENCLOSING A LAGOON 



It is thought that the coral polyps began their growth 
on the slopes of the volcanic peaks, and that the latter 
gradually subsided until they were covered by the sea. 
But while the peak was slowly sinking the coral polyps 
steadily built their reefs upward, keeping the top always 
even with the wash of the waves. This opinion, first made 
prominent by Darwin, is borne out by the fact that, while 
the coral polyp cannot live more than twenty fathoms 



50 PHYSICAL GEOGRAPHY 

below the surface of the sea, the feet's sometimes extend 
almost vertically to a depth of several hundred fathoms. 

In other instances it seems certain that the accumulation 
of marine remains raised the ocean floor to a level upon 
which the coral polyp could live and grow. Whatever 
"building" may have been clone above the surface of the 
reefs and islands, is the work of the waves. 

As a rule, these islands consist of an irregular ring of reef 
waste, broken and tossed up by the waves. The reef is callei I 
an atoll; the enclosed water a lagoon. Usually the atoll is 
broken in one or more places, and the lagoons may form 
good harbors. The reef is rarely more than a few feet high, 
and its vegetation is confined to a few species, main])- of 
palms. 

The Sea. — The sea covers more than half the northern 
and about seven-eighths of the southern hemisphere. 
For convenience, it is also assumed that the edge of the 
continental plateau, and not the actual shore line of the 
continent, is the rim of the ocean basin. Although the 
area covered is continuous, the continents separate it into 
great divisions called oceans. Name them. The polar 
circles are taken as the boundaries of the polar oceans, and 
the equator conventionally divides the two largest oceans 
into northern and southern divisions. 

The Pacific Ocean comprises about one-half the entire 
Sea; the Atlantic about one-quarter. The shore line of the 
latter, however, is considerably longer; explain why. 

In general, the average depth of the oceans varies with 
their size — the larger the ocean the greater its depth. The 
Pacific is about 2,500 fathoms, the Atlantic and Indian not 
far from 2,000 fathoms. The polar oceans are shallower, 
but not enough is known about their depth to compare 



LAND AND WATER 51 

their average. The greatest ocean depths are much in 
excess of the average depths. 

There is a large 3,000-(athom area in the north Pacific and several 
smaller areas in the Atlantic and Indian Oceans. The deepest soundings 
so far obtained are 4,655 fathoms by the U. S. S. Tuscarora, east of 
Japan, in an area now known as Tuscarora Deep; 5,147 fathoms, one 
hundred miles E. N. E. of Sunday Island; and 5,155 fathoms a few 
leagues east of Macarthy Island, not far from the Kermadec group. 
The two last were made by Commander Balfour, H. M. S. Penguin. 
North of Puerto Rico a sounding of 4,651 fathoms has been obtained. 
The cable ship Nero reported a sounding of 5,200 fathoms east of the 
Hawaiian Islands. Formerly deep-sea soundings were made with heavy 
Manila rope, and in very deep water it was impossible to tell when 
the sinker had reached bottom. With the method perfected by Ad- 
miral Belknap and Captain Sigsbee, steel piano wire takes the place of 
the rope. The wire carries at its lower end a sinker which detaches 
itself on touching bottom, at the same time closing a cup that secures 
a specimen of the bottom. Very few of the deep-sea soundings made 
prior to 1870 are now considered trustworthy. 

The greatest depth of the sea scarcely surpasses the 
height of the loftiest mountain peak; yet while four-fifths 
of the sea basin is six thousand feet deep, less than a tenth 
of the land reaches six thousand feet above it. 

The floor or bed of the sea is by no means so irregular 
as the surface of the land; and, the vicinity of the coral 
islands and the continental shores excepted, no steep slopes 
or abrupt changes of level are known to exist. The sound- 
ings made for the telegraph cables disclosed no slopes nor 
inclines too steep for a railway grade. After deep water 
was reached, the soundings for the Atlantic cable of 1866 
did not vary more than seven or eight hundred feet in two 
thousand miles. 

Arms of the Sea. — In places the sea extends a consider- 
able distance into the outlines of the continents, forming 
seas, gulfs, bays, estuaries, etc. Many of the smaller coves 



52 PHYSICAL GEOGRAPHY 

arc shore formations, having boon made or shaped by the 
action of waves or b}' currents of water. The larger arms 
are structural, and have resulted from upheaval or de- 
pression of the coast of the continent. 

The borders of a continent may be flanked by lofty 
highlands, and the trend of the coast usually conforms to 
the trend of the ranges. Thus, the highland that gives to 
the west coast of Africa its shape also gives a similar form 
to the Gulf of Guinea. Where parallel ranges extend sea- 
ward, the sea usually enters the valley between them. On 
a map of North America, note the position of the Gulf of 
California, and Puget Sound; on a map of Europe, the Adri- 
atic and Baltic Seas. Similar examples occur along the 
west coast of Asia. 

A partly enclosed portion of an ocean is called a sea, 
and the Caribbean and North Seas are examples of a type 
of enclosed waters. Of this type the Mediterranean Sea 
is a noteworthy example, and such arms of the ocean are 
often called mediterraneans. Such indentations as the Gulf 
of Mexico, Hudson Bay, the Gulf of California, etc., are 
properly included in this class." Nearly all the larger arms 
of the sea are depressed parts of the continents, or of the 
plateau on which they are situated. 



Color names are of frequent occurrence in the nomenclature of the 
arms of the sea. The color of sea-water is both apparent and real. The 
apparent hue is often due to reflection from the sky; the real color to 
the substances in solution. Shallow water is commonly greenish; deep 
water a dark blue. The water of the Gulf Stream has a peculiar blue 
color and is instantly distinguished from the lighter colored water on 
either side. The phosphorescence of sea-water, usually observed in warm 
regions, is due to a microscopic organism, Nocliluca miliaris, that, like 
the common firefly, has the power of emitting light. At times the wake 
of a vessel seems a track of lire. 



54 PHYSICAL GEOGRAPHY 

Coast Forms. — The study of shore outlines shows thai 
various parts of the coast differ materially. A striking 
difference may be observed in comparing the coasts of 
Maine and Florida. The illustrations on pp. 48 and 53 are 
also examples of shore forms. One of them, a rock-bound 
coast deeply indented with fjords and hemmed in by rocky 
islets, has been worn and frayed by the action of glacial 
ice; it has also subsided until the valleys are submerged 



A CLIFF-GIRT COAST, SAN JUAN, PUERTO RICO 

by the sea. Name the various coasts that resemble ii. 
Are they situated mainly in high or in low latitudes? 

In the illustration on p. 55, the plain bordering the sea 
dips so gently below sea-level that the water is shallow half 
a mile or more from the shore. The drag of the waves roll- 
ing in and combing on the coast picks up sand and rock 
waste brought down by muddy streams and piles it in the 
form of long spits and beaches at a little distance from the 
shore. Find other coasts that resemble it. 

Marine currents frequently attempl to carry away the 
rock waste piled up by the waves; as a result, it is dragged 



LAND AND WATER 



55 



into a curved form making a hook. Sandy Hook, New 
Jersey, is an example. 

Sinking Coasts. — Along many parts of the coasts the sea 
is encroaching on the land. The waves beat against the 
shore, breaking .it away 
until the latter has be- 
come a high cliff. This, 
in turn, is undermined 
with each successive 
storm and, as the cliff 
is battered down, the 
rock waste composing it 
is swept away by the 
waves and currents. 
The west end of Long 
Island and the Jersey 
shore at Long Branch 
have suffered in this 
way, and buildings have 
been repeatedly moved 
farther inland in order 
to save them. Much of 
the coast around the 
Gulf of Mexico, the Zuy- 
der Zee, and the "delta 
of the Ganges-Brahma- 
putra is sinking. The coast of the New England Plateau 
has subsided until the sea has flooded the former coast 
plain and the lower valleys. 

The east and south coasts of the British Isles have lost to the sea 
an aggregate of several hundred square miles. On one part of the 
Cheshire coast the sea has advanced about 2,000 feet within a century. 




A STRETCH OF NORTH CAROLINA COAST 

The barrier beaches nearly enclose the coast; the in- 
lets are kept deep enough lor navigation by the 
tidal currents. The estuaries are drowned river- 
mouths. 



56 PHYSICAL GEOGRAPHY 

The site of Ravensburg, once a city as large as Hull, is now covered 
many fathoms deep, and a similar fate almost befell Dunwich. A 
few centuries ago about two miles of forest lay between the city and the 
sea. In 1677, however, the waves had removed all the intervening 
land and had battered down the market. A few years later St. Peter's 
Cathedral was engulfed. Of Wales, Professor A. G. Ramsey says: 
"More land has gone into the sea than now remains above sea-level." 

As the land sinks, the river mouths become broad 
estuaries, and the coast lowlands and valleys are converted 
into coves, bays and sounds. " Drowned " valleys are there- 
fore an indication of a sinking, or sunken coast. New 
York Bay and the lower Hudson form a remarkable ex- 
ample of a sunken coast and drowned valley. The old 
channel of Hudson River has been traced more than eighty 
miles outward from the present mouth. Chesapeake Bay, 
Delaware Bay, and the estuaries opening into Pamlico 
and Albemarle Sounds are also examples. In Holland, 
where subsidence is going on, the dykes and revetments 
that protect the cultivated lands from inundation have 
been more than once increased in height. 

Drowned valleys and estuaries usually contain good 
harbors, and most of the great seaports of the world 
have been built at convenient places on their water fronts. 
The drowned valleys of the North Atlantic coast of the 
United States contain the ports through which about 
ninety per cent, of the foreign commerce of the country is 
carried. 

Rising Coasts. — Along a considerable part of the 
California coast there are evidences of elevation that has 
been both recent and rapid. Former sea beaches are 
found several miles inland and, imbedded in their sands are 
shells and the bones of marine animals that belong to a 
recent period. In one part of Alaska the upheaval has 



LAND AND WATER 



57 



been so recent and rapid that marine shells are still clinging 
to the rocks. 




AN UPLIFTED COAST, SAN PEDRO, CAL. 

From a survey made by Merick Reynolds, Jr. The successively formed beaches are shown by 
the strata of shells and sand. 

At San Pedro, California, the upward movement has been unusually 
rapid. Several layers of shells mixed with sand are found one above 
another, at heights varying from five to fifteen feet or more. The shells 
belong to species some of which are not now extinct, and most of them 
have been preserved in their natural state. The highest beach is nearly 
three hundred feet above sea-level. The various beaches are so slightly 
weathered that they seem scarcely altered. 

Coral Formations and Coast Outlines. — Coral forma- 
tions are important factors in shore lines and usually they 
are associated with sinking coasts. On shore they are 
called fringing reefs; farther out, barrier reefs. Almost the 
entire east coast of Australia is shut off from open com- 
munication by a barrier reef more than twelve hundred 
miles long. There are a few channels across the reef, but 
it is nevertheless a great obstacle to commerce. Fringing 
reefs occur on the south coast of Florida, and are- perhaps 
the most common examples of coral formation. They are 
common along the shores of the Bahama Islands, and occur 
along the Hawaiian coast. 

Coral growths are confined to warm, littoral waters, and 
the reef-building polyp is limited to waters whose temper- 
ature does not fall below 25° (67° F.). Absolutely clear 



58 PHYSICAL GEOGRAPHY 

water is requisite, and for this reason coral reefs arc rarely 

found along the .shores of continents, and never within the 
reach of river sediments. 

Coast Outlines and Civilization. — The coast forms of 
a country have not a little bearing on its prosperity and 
its enlightenment as well. A coast with good harbors in- 
vites commerce and intercommunication. Al< >ng the North 
Atlantic coast of the United States, where a rugged surface 
slopes abruptly below sea-level, good harbors are numerous. 
The same conditions prevail on the coast of Europe. Com- 
merce and intercommunication always seek a region having 
good harbors. Africa and South America have but very 
few good harbors, and to this fact the half-savage condi- 
tion of the native tribes is largely due. 

QUESTIONS AND EXERCISES.— Which of the oceans is nearly 
landlocked? 

At what place do the Pacific and the Arctic Ocean meet? — the 
Atlantic and the Arctic? 

Compare the coast of Europe with that of Africa, with respect to 
its regularity; which has the greater length of coast line? 

How have good harbors affected the progress of the English people? 
What has been the effect of closed ports on the Chinese? 

Compare the commerce of the North Atlantic coast of the United 
States with that of the South Atlantic coast. To which type does each 
of these coast forms belong? Where are most of the large seaports of 
the Atlantic coast of the United States? Explain the reason for their 
location. 

Why should Australia be considered a continent rather than an 
island? 

Does the cutting of the Suez Canal give Africa any insular properties 
that it did not possess before? 

Make a list of the principal mediterranean seas of the world. 

Mention several instances in which peninsulas enclose waters so as 
to form gulfs or bays. 

From a good map of the British Isles find the names used as syn- 
onymes of " cape " and " strait." 



LAND AND WATER 59 

Find the centre of each hemisphere on p. 41. 

Study the position of the submerged part of the continents on the 
map, pp. 44-45- 

COLLATERAL READING 

Dana. — Manual of Geology, pp. 145-152. 

Redway. — New Basis of Geography. Chapter IV- 

Shaler. — Sea and Land, pp. 187-222. 

United States Geological Survey. — Norwich and New London 
Sheet (drowned valleys) ; Sandy Hook and Barnegat Sheets (spits and 
barrier beaches); Port Washington Sheet (cliffs). 



CHAPTER IV 

THE RESULTS OF SLOW MOVEMENTS OF THE ROCK 
ENVELOPE: PLAINS, PLATEAUS, AND MOUNTAINS 

The larger vertical forms of the land are the results of 
the slow movements of the rock envelope. Any consider- 
able area of land but little higher than sea-level is called 
a plain; if considerably higher, a plateau; if wrinkled, 
folded, and broken, a mountain system. There is no fixed 
elevation at which an area ceases to be a lowland, or vice 
versa, but in general, surfaces more than two thousand feet 
above sea-level are called highlands, while those of less alti- 
tude are lowlands. 

As a rule, the various features that constitute topogra- 
phy are distinct one from another; but in many instances 
lowlands gradually increase in altitude and become high- 
lands; an almost imperceptible swell in a level plain may 
develop into a cliff or a ridge; and a mountain-range, little 
by little, may lose its characteristic form among other 
features of the landscape. So it often happens that a sin- 
gle topographic form may have the character of several 
kinds of relief. 

Plains. — Any level or nearly level stretch of land is 
commonly called a plain. Most plains are lowlands, but in 
a few instances the name is applied to surfaces that are 
more than six thousand feet above sea-level — an elevation 
considerably greater than that of some mountain-ranges. 
The plain east of the Rocky Mountains is an example; 

60 



PLAINS, PLATEAUS, AND MOUNTAINS 61 

it is higher than the crests of the Appalachian Mountains, 
and about as high as the highest peaks. In fact, no exact 
limit fixes the altitude of a plain, although an elevation of 
two thousand feet is sometimes conventionally employed. 
Plains are variously named. The grassy plains of the 
New World were named savannas by the Spanish, and 
prairies by the French — both of which names are still 
commonly employed. In South America the vast plains 
of Argentina are called pampas; the grassy plains of the 




A ROLLING PLAIN, VIRGINIA 
// is now a peneplain. The forestry is deficient, and the soil only moderately fertile. 

Orinoco, llanos; and the forest-covered plains of the Ama- 
zon, silvas. In Eurasia, the vast plains that almost girdle 
the Arctic Ocean are known as steppes, their frozen, swampy 
coast fringe being known as tundras. In England and 
Scotland the terms, meadow, heath, and moor, are used. 



62 PHYSICAL GEOGRAPHY 

The difference in the surface features of these plains is due to tat itude, 
altitude, and rainfall. The pampas somewhat resemble (lie high plains 
east of the Rocky Mountains. Both slope from a high to a low level, 
and both are covered with "bunch-grass." The llanos are watered 
by periodical rains and are alternately a swamp and a sun-baked desert. 
The silvas lie in a region of almost constant equatorial rains; hence 
they are adapted to tropical forest growth. The pampas and llanos 
produce wild cattle and horses; the silvas, rubber and ornamental 
woods. 

Formation of Plains. — Most plains have been formed 
by the action of water, or have received their surface 
configuration by it. If formed by the uplift of a former sea 
margin they are known as marine, or coast plains; if old 
lake bottoms, they are lacustrine plains. The sediments 
deposited by running streams become alluvial plains; those 
levelled by moving ice, diluvial plains. 

Coast and Marine Plains. — Probably every part of the 
earth's lowland plains at some period of their existence 
have been a part of the sea bottom. The waves which 
batter the shores of the continents and the running waters 
that sculpture the land are constantly accumulating ma- 
terial along the shores. Waves and currents scatter and 
level this rock waste; in time an uplift raises it above sea- 
level, forming a gently sloping plain. Because of its posi- 
tion along the coast it is called a coast plain. Such a plain 
situated at a considerable distance inland is sometimes 
called a marine plain, but nearly every marine plain was 
a coast plain at the time of its formation. If there be deep 
water along the shore, the coast plain is apt to be narrow; 
on the other hand if the plain has been formed by a gradual 
uplift of a part of the continental shelf, it is apt to be broad. 

Practically the whole Atlantic coast of the United States 
is bordered by a coast plain. North of New York Bay it 



PLAINS, PLATEAUS, AND MOUNTAINS 63 

is narrow, but south of the bay, where the continental shelf 
is broad, its breadth is over two hundred miles. The line 
where the coast plain joins the foothills or "piedmont 
lands" is called the Fall Line. East of this line the rivers 
broaden into navigable estuaries; falls and rapids at or 
near the heads of the estuaries furnish a considerable water 
power. As a result of these two features a dozen or more 
important cities have been built along the Fall Line. The 
Gulf Coast plain is somewhat more complex; it consists of 
several blocks or "cuestas," each of which is a coast plain 
of separate formation. 

The Baltic coast plain consists of land that once formed 
a part of the bed of the Baltic Sea. Much of its top layer 
consists of wind-blown sand, mixed with fertile loam. It 
is remarkable in one respect : it is the best known region in 
the world for the production of the sugar beet. 

The great Russian plain is the largest in the world. Its 
situation, however, is unfortunate from an economic stand- 
point. The northern part of the plain is too cold for the 
growth of foodstuffs and much of it is a tundra, producing 
nothing but coarse mosses. In winter it is ice-covered; in 
the short arctic summer it is an impenetrable morass. 
The central part is a peneplain, or much worn surface, 
that may be called an "old" plain. 

The prairies of the Mississippi basin are marine plains. 
In the central and southern part much of the old sea-bed 
has been covered by the deposits of fresh water and brackish 
lakes that once existed there; the northern part is covered 
with a drift deposited by the melting waters of glaciers. 
To this drift its fertility for food crops is largely due. It 
produces about one-quarter of the world's wheat, and about 
three-quarters of the maize, or Indian corn. 



64 PHYSICAL GEOGRAPHY 

The region east of the Rocky Mountains, known as the 
"Plains" is an elevated plain that is properly a plateau. 
Much of its surface is covered deep with wind-blown rock 
waste. But the streams of the Rocky Mountains arc cutting 
their channels well below the surface. Here and there are 
alluvial plains formed by rivers of a previous age. The 
newer streams are now carving their valleys into the older 
courses. In places this region has been greatly sculptured. 
Such lands of this region as can be irrigated produce alfalfa, 
macaroni wheat, sugar beets, and fruit. 

Lacustrine Plains. — Lacustrine plains are the level 
floors of old lake basins, or the margins of lakes that have 
greatly shrunken in size. Such a plain may have come into 
existence in any one of several ways. A notch may have 
been cut in the rim of the basin, causing the water to flow 
off; the rainfall may have decreased so that water of the 
lake disappeared by evaporation; river sediments and 
vegetation may have filled the basin. 

One of the finest examples of lacustrine plains is the 
valley of Red River of the North. This plain resulted from 
the draining of a lake, and so recently was it formed that 
the surface is scarcely notched by the river that now 
imperfectly drains it. 

The plain surrounding the Caspian Sea is an excellent 
example of a plain in the process of formation. On the 
northern side, the gradual shrinkage of the lake has left a 
plain more than two hundred miles wide, and this increases 
in size as the lake shrinks. The valley or basin of Great 
Salt Lake is passing through a similar period of develop- 
ment. 

Alluvial Plains. — Alluvial plains are best developed 
along the lower courses of rivers, although they exist in 



PLAINS, PLATEAUS, AND MOUNTAINS 65 



narrow reaches along almost the entire length of the stream. 
The bottom-lands of the lower Mississippi and the Danube; 
the mazy deltas of the Nile and the Ganges-Brahmaputra, 
and the broad, fertile plains of the Po are examples. 
Name other illustrations. 

Alluvial plains are among the most productive lands in 
the world. Because their soil is constantly replenished 



~Msy<*':--* l 




'":;"•' 



A PRAIRIE PLAIN, KENTUCKY 
A very fertile plain with a considerable forest 

by overflows and freshets, they rarely wear out; the nutrient 
elements are supplied about as fast as they are exhausted. 
Distribution of Plains. — Alluvial and lacustrine plains 
are incidents in the physiography of rivers and lakes; and 
coast plains are formed on nearly all shores. The great 
plains of the world are mainly on the slopes of the Arctic 
and the Atlantic Oceans. From west to east the Russian 



66 PHYSICAL GEOGRAPHY 

plain stretches a distance of about nine thousand miles; 
from north to south, about three thousand miles. In Asia 
it is high and rolling; in Europe the greater part is low and 
comparatively level. 

In the northern part of North America it loses many of 
the topographic features of a plain and, in places, is a low, 
but rugged plateau. Its slope, like that of the Eurasian 
plain, is toward the Arctic Ocean and, like the latter, its 
coastal portion is bordered by tundras. Generally con- 
sidered, the great Arctic Plain is the rim of a vast basin 
that almost shuts the Arctic Ocean from the rest of the sea. 

In the New World the great continental plain extends 
from the Arctic Ocean to the Gulf of Mexico, and there is 
an apparent extension from the Caribbean Sea southward 
through South America. Its continuity is broken by 
occasional ranges and arms of the sea. It presents cer- 
tain marked contrasts to the plain of the Asian Continent. 
The latter extends east and west; the former, north and 
south. The latter is a margin of the continent; the for- 
mer is an interior plain, bordered by mountain ranges. 

Physiographic Aspect of Plains. — Plains are quite 
as subject to the weathering processes of nature as are 
mountains and plateaus but, because of their gentler slopes, 
the wearing process is not so rapid. Water is the chief 
agent in their formation; it is likewise the chief factor in 
their destruction. From the moment a plain conies into 
existence, storm waters and running streams begin to 
carve channels in its surface. These waters extending in 
area, carry the greater part of the surface material away. 

A plain thus channelled is said to be "dissected." That 
part of the South Atlantic and Gulf coast nearest the sea 
is young. Its slope is so gentle that the streams have not 



PLAINS, PLATEAUS, AND MOUNTAINS 67 

yet carved their channels to any great depth. Nearer to 
the piedmont lands it is older and therefore has been much 
more dissected. The more nearly the dissected plain 
approaches a level surface the slower is the process of its 
wasting. A plain that has been first dissected and then 
worn down is called a peneplain. 

The plains bordering Lakes Erie and Ontario show signs 
of greater age. The streams have accomplished much 
dissection and the channels are deep. The "Bad Lands" 
of South Dakota and Nebraska are remnants of an old 
lacustrine plain that has been so greatly dissected that the 
region is well-nigh impassable. 

Economic Value of Plains. — Because of their com- 
paratively level surface, plains are more accessible to 
commerce and more easily cultivated than mountainous 
regions. Railways can be built across them at the minimum 
of cost, and the larger rivers that traverse them are usually 
navigable. 

Moreover, their soil is usually deep and fertile. There- 
fore they are capable of supporting a denser population 
than mountainous regions. In remote times the alluvial 
plains of the Nile and of Mesopotamia were the seats of 
dense population and vast industries. In later times the 
plains of Europe and of the United States have become 
the great producers of wealth. It may be said, therefore, 
that the greater part of the world's wealth and power is 
centred in the plains of the temperate zones. About ninety 
per cent, of the world's population lives below the altitude 
of 1,000 feet. Only a small fraction of the world's popula- 
tion lives above the altitude of 2,000 feet, and but few of 
the great cities are more than six hundred feet above sea- 
level. 



68 PHYSICAL GEOGRAPHY 

Plateaus. — A broad extent of country having an eleva- 
tion of a thousand feet, and an irregular or dissected sur- 
face, is called a plateau. The name, originally n leaning 
"flat," or "level," has acquired an almost opposite signifi- 
cation. A level plateau of small area is usually called a 
mesa, a table-land, or a table-mountain, according to its 
general form and structure. 

Like most other elevations of the earth's surface, pla- 
teaus are a result of the gradual uplift of parts of the rock 
envelope. Most of the great plateaus of the earth are 
rimmed by lofty mountain-ranges, and their surfaces are 




A DISSECTED PLATEAU, JOHN DAY VALLEY, OREGON 

The sheet oj lava at the surface has been removed here and there, leaving a series oj mesas. 

generally traversed by ridges and valleys. Thus, the pla- 
teau region of western North America, nearly a mile and a 
half high, is bordered by the lofty Rocky and Sierra Nevada 
mountain ranges; the great Bolivian plateau is edged by 
the highest summits of the Andes; and the highest plateau 
in the world, that of Tibet, is rimmed by some of the loftiest 
ranges of the earth. 

Many mesas or table-lands are the result of unequal 
weathering. The top of the mesa is commonly a layer of 
rock resting upon softer substance. The latter is pro- 
tected from the action of the elements by the harder mate- 
rial and, in time a table-land is formed. As a rule, such 
table-lands are the outlying or isolated remnants of pla- 
teaus. They are noticeable objects because of their flat 



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Echo Cliffs 



70 PHYSICAL GEOGRAPHY 

tops and the steep cliffs or escarpments thai form their 
slopes. 

A high plateau sparsely covered with vegetation is much more readily 
dissected by streams than a grass-covered surface. The region through 
which the middle course of the Colorado River flows is an example. 
Here the plateau has been cut to a depth ranging from three thousand 
to six thousand feet. Only a small part of the plateau has been re- 
moved, and large areas show as yet but little of dissection. In other 
parts, however, such as the "Land of Standing Rocks," denudation 
has been considerable, and only the towers that are remnants of harder 
rocks remain. 

Distribution of Plateaus. — The highest plateaus arc 
in the great highlands that face the Pacific and Indian 
Oceans. The lesser highlands that border the Atlantic 
Ocean also contain plateaus. If the highlands border the 
sea, the plateaus may take the form of peninsulas; name 
several examples on the map of Asia. 

Among the plateaus of the Asian Continent, that of 
Tibet is remarkable for its size and height, being nearly 
three miles above sea-level. To the westward are the 
Pamirs, a series of grassy plateaus, like the "parks" of 
Colorado, about three and a half miles above sea-level. In 
North America, the plateaus of the western highlands are a 
little more than a mile high, while those of the eastern high- 
land have less than half that altitude. In South America 
the plateaus of the Andes are about two miles high, while 
those of the eastern region have less than one-third that 
height. 

Economic Aspect of Plateaus. — As a rule, plateaus are 
arid regions; they are therefore not so productive as low- 
land plains. In some instances they are so high that but 
little rain falls on them; in others the mountain rims shut 
off the moisture that is borne with the winds. The rugged 



PLAINS, PLATEAUS, AND MOUNTAINS 71 

slopes and deep canons almost always make commercial 
intercourse very difficult. Because of their unproductive- 
ness high plateaus, as a rule, are sparsely peopled; and 
because of the lack of intercommunication the civilization 
of the native peoples is seldom of the highest type. 

In the lower plateaus the conditions are different; there 
is generally a rainfall sufficient for the production of food- 
stuffs, and the land that cannot be cultivated is often well 
adapted to grazing; meat, cattle products and wool- 
growing are usually associated with these plateaus. Hides 
are a product of the Mexican plateau; mohair is a specific 
feature of the Bolivian Plateau; merino wool comes from 
the Iberian Plateau; and the best rug-making textiles are 
confined almost wholly to the Plateau of Iran. The New 
England Plateau has a generous rainfall and the rugged 
surface makes it a region of a considerable water-power. 
The broken and dissected rock strata in many instances 
yield minerals and metallic ores useful in the arts and 
sciences, and the rugged character of the surface often 
furnishes an abundance of water-power. 

Mountains. — Mountains are the most characteristic 
and remarkable features of the earth. In form, they are 




A SECTION ACROSS THE UINTA MOUNTAINS 
A single jold with jaull. After Powell. 

great ridges with very rugged surfaces. In structure, 
they are folds or wrinkles in the strata of the rock envelope, 
or else they are immense blocks of rock, broken and partly 
upturned. 



72 



PHYSICAL GEOGRAPHY 



Mountains occur usually in systems, each of which con- 
sists of many ranges. A very extensive system is some- 
times called a cordillera. Thus, the Rocky and Andean 
Systems form the great cordillera of the Western Continent. 
Ranges or folds that seem to be continuous are said to be 
a chain, as the Sierra Nevada and Cascade Mountains. A 
single fold may be worn away so that the broken strata 
form ridges; or the crest may be weathered so unevenly 
that it presents the appearance of a series of notches, 

thereby forming 
a sierra. Any 
part of the crest 
or summit mate- 
rially higher than 
the rest forms a 
peak. Sometimes 
the peak is a high 
crag, or a pinna- 
cle of rock, but 
the name is also applied to volcanic cones. Elevations thai 
properly are plateaus — as Broad Mountain, Pocono Moun- 
tain, and Broad Top, in the Appalachian system — are 
also called mountains. 

Isolated peaks, or "monadnocks," are not uncommon, hut for the 
greater part they occur in mountain ranges that have been greatly 
worn. Mount Holyoke is one of several examples in Massachusetts. 
It was not thrown up in its present form; on the contrary, it was left 
when the rest of the range, being softer, was worn away. Mount 
Monadnock, New Hampshire, a peak that has given its name to the 
type, is a similar example. Isolated ridges or ranges are more common 
than isolated peaks, and excellent examples may be found in the Great 
Basin. In some instances the apparent isolation is due to the fart 
that the ranges are half buried, the exposed upper parts extending from 
a level plain of loose rock waste. 




THE JURA MOUNTAINS 
A series oj gentle jolds, partly worn into ridges. 



PLAINS, PLATEAUS, AND MOUNTAINS 73 

A mountain system is generally of great extent, several 
of the more important exceeding four or five thousand 
miles in length. A range, on the contrary, rarely exceeds a 
few hundred miles in length. It gradually takes form, 
continues a short distance, and then disappears, another 
range to the right or the left taking its place. The rolling 
hills that form the approach to a system are called foot- 
hills or, better, piedmont lands. The hollow or depression 
between adjacent ranges forms an intermontane valley; or, 
if wide and nearly enclosed, a park. A valley that extends 
across the range is called a pass, a gap, or a canon. 

Structure of Mountain Ranges. — In the simplest form, 
as in the Uinta Mountains, there is a single fold; in the Jura 




■'J&ry 



SECTION OF A DISSECTED RANGE 
A single fold is dissected into a number o] ridges. 

Mountains there are several; in the Rocky Mountains there 
has been a mashing and crumpling of the strata, producing 
irregular and complex results as though the leaves of a book 
had been pressed and crumpled sideways by a tremendous 
force. 

The process of uplift and folding takes place so slowly 
that it cannot be measured except after long intervals of 
time. This is shown by the conduct of certain rivers that 



74 PHYSICAL GEOGRAPHY 

flow across the folds. The streams cut their channels 
downward quite as fast as the folds are pushed upward. 
So when the fold has become a lofty range, it is severed 
transversely by the stream. 

Excepting the core of granite, or similar rock that is 
present in the lower part of many folds, mountain-ranges 
are composed of strata of sedimentary rock. Moreover, it 
is a notable fact that the strata which form them are much 
thicker along the folds than elsewhere. Thus in the 
Appalachian Mountains, the sediments composing the folds 
are about 40,000 feet thick, while the same strata in the 
Mississippi Valley are scarcely more than 4,000 feet in 
thickness. Not only were the deposits that became sedi- 
mentary rock thicker before the folding took place, but 
they were made still thicker by side pressure and crump- 
ling. 

The ideal system with its parallel folds exists; but in 
general,, mountain architecture is very complex. The 
system, in fact, consists of a tangle of ridges and ranges so 
greatly worn by the weathering forces of nature, that in 
many instances it is difficult to trace their real direction. 
Not infrequently several ranges seem to radiate from a 
marine uplift, as in the case of the Pamir highland, from 
which radiate the ranges of the Himalaya, Tian Shan, 
Hindu Kush, and Suliman folds. 

Block Mountains. — Not all ranges present the aspects 
of folds. The ridges in the Great Basin of the United States 
are great blocks of sedimentary rocks that, having been 
broken and tilted, are left with edges partly upturned. The 
Sierra Nevada and Cascade Ranges are both folded and 
broken, and their abrupt eastern slope is the edge of an 
immense block tilted upward from the Pacific. 



PLAINS, PLATEAUS, AND MOUNTAINS 75 

The folds of the strata take various names, according to the position 
of the rocks. Thus, a bend in the rock layers that forms a trough, is 
a synclinal, valley; if the bend is upward, so as to form a ridge, it is an 




BLOCK MOUNTAINS, BASIN REGION 

The upturned edges o) the great blocks jorm the ranges. 

anticline, and a valley along the crest as its upper surface is an anti- 
clinal valley; both are illustrated in the Jura Mountains (p. 72). A 
valley formed by broken and tilted strata, such as those of block 
mountains, is a monoclinal valley. A break in a stratum, or of several 
strata, in which there is a displacement so that one side is higher than 
the other constitutes a fault. 

Physiographic Aspect of Mountains. — From the mo- 
ment the process of uplift commences, the waters of the at- 
mosphere begin to level off the folds. The more prominent 
a topographic feature is, the more exposed it will be to the 
factors that destroy it; and although every part of the land 
undergoes wearing, the higher surfaces generally suffer most. 
As the process of elevation goes on, the mountain torrents 
carve the slopes of the range, diversifying it with valleys, 
canons, ridges, and hogbacks. 

At the mouth of every canon there is usually a fan-shaped pile of 
coarser material, carried thither by running water, called talus. A 
pile of talus is usually found at the bottom of every steep, rocky cliff. 
It is an example of cliff waste. 



76 PHYSICAL GEOGRAPHY 

Not only are the slopes of the ranges sculptured, but the 
crests are also worn away. The tops of the folds are 
broken and, little by little are removed, leaving the up- 
turned edges of the strata in the form of long ridges. Most 
of the ridges of the Appalachian Mountains are formed in 
this manner; there are few folds, but many ridges. 

The amount of material removed from the slopes and 
crests of mountains is enormous. The crests of the Ap- 
palachian folds in Pennsylvania are scarcefy more than 
two thousand feet high at the present time; but if all the 
material that has been removed could be again heaped 
upon them., their summits would be more than ten miles 
high. 

In many instances, notably in the Appalachians, the ridges are the 
floors of old valleys. The latter were firmer than the broken crests 
of the folds, and therefore were better able to resist disintegration and 
erosion; consequently the crests of the folds in time were worn down to 
a level lower than that of the original valleys. 

Probably most of this material has been removed by 
running water, but the moving ice sheet that at one time 
covered the northern part of the Appalachian highlands was 
also a powerful agent in sculpturing their crests and 
slopes. In New York, where they received the full force of 
glacial ice, the highlands are worn down to base level. In 
Pennsylvania, where the wasting was less effective, they are 
about two thousand feet high. But in the South Atlantic 
States, beyond the limits of glacial ice, the ridges are more 
than four thousand feet high. 

The Catskill and Adirondack groups were apparently 
severed from the system during the glacial epoch. The 
former have been cut so deeply by si renins that they are 
now ridges extending east-west in direction. The summits 



PLAINS, PLATEAUS, AND MOUNTAINS 77 

at the Adirondack peaks were probably higher than the 
surface of the glacial ice sheet. 

As a rule, mountain-ranges which show but few effects 
of weathering are comparatively young. The tilted blocks 
that constitute the ranges of eastern Oregon are scarcely 
notched by streams, and are very slightly weathered. The 
ridges of Nevada are greatly weathered and carved, and 
the Rocky Mountains, though young as compared with the 
Appalachian folds, are much worn. 

The Laurentian folds, among the oldest in North Amer- 
ica, are likewise worn nearly to base level. The Huronian 
ranges about Lake Superior are worn down nearly to the 
level of the surrounding land. They may therefore be 
called relict mountains. 

The character of the weathering, and the landscape, 
depend partly on the character of the rock and partly on 
conditions of climate. In the Appalachian ranges all the 
forms are rounded, subdued, and graceful. In arid regions 
they are apt to be angular. The notched crests of western 
ranges of the United States and Mexico have suggested the 
name "sierra" {saw), the sharp, enduring crags of the Alps, 
"aiguille" {needle), "horn," and "dent" {tooth). 

Distribution of Mountains. — Mountain-ranges are inci- 
dental chiefly to highland regions. The great highlands 
that border the Pacific and Indian Oceans are rimmed 
throughout much of their extent by lofty folds. In North 
America the Rocky and Sierra Nevada ranges are the rims 
of a high plateau whose surface is traversed by block ranges. 

The great system of southern Europe, extending from 
the Caspian Sea to the Atlantic, belongs to the principal 
highland of Eurasia. The Alps form the northern, and the 
Atlas ranges of Africa the southern rim. What sea fills the 



78 PHYSICAL GEOGRAPHY 

intermontane valley? A partly submerged chain extends 
along the east coast of Asia; name the peninsulas and 
principal island groups belonging to it. The great systems 
are nearest the Pacific and Indian ( Oceans. 

Intermontane Valleys. — The folding of strata into 
parallel ranges naturally forms valleys between them, and 
these may be termed original valleys. The great inter- 
montane valley of California, Oregon, and Washington is 
of this character. Name the ranges between which it is 
situated. Although interrupted by cross ranges it prac- 
tically extends from Puget Sound to the Gulf of California. 
The valley, a part of which the St. Lawrence River now 
occupies, is similar in structure. A great valley extends 
along the eastern part of Africa from north to south; it is 
known as the rift valley. 

In a few instances the cross spurs that join parallel 
ranges enclose valleys of considerable extent. The Parks 
of Colorado, and the Pamirs, both frequently classed 
among plateaus, are examples. The latter are situated in 
a high mountain knot which, because of its great height, 
is often called the "Roof of the World." 

Stream Valleys. — The valleys and canons formed by 
running water are due to slopes that are more or less steep. 
They are not a part of mountain structure, but are a result 
of it. Such valleys are most common in mountainous 
regions and in plateaus. 

Most valleys show the results of stream-cutting and the 
weathering action of water. Shenandoah Valley, the de- 
pression crossing Virginia, is an example. The rocks along 
the line of the valley were more easily worn away than those 
to the east and the west, and hence the valley resulted from 
their removal. 



PLAINS, PLATEAUS, AND MOUNTAINS 79 



The water may wear the rocks at the crest of a range 
more easily than it can remove them at other places. In 
this way canoe-shaped valleys are formed at the summit of a 
fold. More commonly, however, the streams on opposite 




ill 

mm 



CANOE VALLEYS, APPALACHIAN MOUNTAINS 

sides of a range wear their channels to the crest, making 
deep notches across it. Some of the passes in the Sierra 
Nevada and Rocky Mountains are examples; and so, too, 
are the gaps of the Delaware, Susquehanna, and Hudson 
Rivers. If at a level with the base of the range, such 
transverse valleys are commonly called water gaps; if at a 
considerable altitude, they are passes. 

Among famous passes are Argentine, 13,100 feet, the highest wagon 
road pass in the world; Marshall Pass, 10,900 feet, one of the highest 
railway passes in the world; Alpine Pass, 13,550 feet, and Mosquito 
Pass, 13,700 feet — all in Colorado. Simplon, St. Bernard, and Brenner 
are famous passes across the Alps, and for centuries they have been 
highways of commerce. A railway pass in the Andes is nearly 14,000 
feet above sea-level. 

In many instances the pass is not fully surmounted ; instead of build- 
ing the railway over the divide, it is more economical to construct 
a tunnel under it. Some of these tunnels are marvels of engineering 
skill. St. Gotthard and Mont Cenis tunnels have been driven through 
the Alps; Hoosac tunnel pierces the range of the same name in Mas- 
sachusetts; San Fernando tunnel, in California, and the tunnel of the 
Transandine Railway are examples ; each is one mile or more in length. 

In other cases the railway surmounts the range by zigzags, or by long 
and intricate loops, crossing and recrossing itself through tunnels that 



80 PHYSICAL GEOGRAPHY 

often are sharply curved. Near Caliente, California, the Southern 
Pacific Railway is built in sinuous loops aggregating about twenty 
miles in order to cross a divide scarcely two miles from the head of the 
valley. The famous loops of the Colorado Midland over Hagermans 
Pass is also a well-known example of the railway builders' skill. 

Economic Aspect of Mountains. — Although moun- 
tains are sparsely settled, and include a veiy large area of 
uncultivable land, they nevertheless exert a great influence 
on life. Ranges that face rain-bearing winds may be lofty 
enough to intercept the moisture, so that little or none 
falls on the leeward side. How does this affect the habit- 
ability of the region west of their summits? In various 
localities the ranges chill the winds that pass over them 
and condense moisture that otherwise would not be pre- 
cipitated. Mountains, therefore, are factors in the dis- 
tribution of rain. 

The broken folds of the strata frequently expose metals 
and minerals that otherwise would not be accessible. Al- 
most all the gold and silver come from mountain-ranges; 
and so, also, does most of the copper. Practically all the 
anthracite coal and much of the best iron ores are associated 
with the rocks of mountain-ranges. The latter are, there- 
fore, essential to the industries of mankind. 

Because of the difference of climate on opposite sides 
of high ranges, the distribution of species is restricted. 
The dense forests of the Pacific coast cannot extend across 
the Cascade and Sierra Nevada Ranges, because there is 
not enough moisture to support them. On the other hand, 
not many of the plants of the arid side can cross the ranges 
and survive because climate and soil are unsuitable. 

Mountains as Factors in History. — Mountains affect 
life and its industries also because they are barriers to 
intercommunication. The Greek peoples of early times 



PLAINS, PLATEAUS, AND MOUNTAINS 81 

found it much easier to spread along the shores of the 
Mediterranean and across the iEgean Sea than to cross the 
Balkan Mountains. For the first fifty years of our national 
history there was no transcontinental intercourse between 
the Atlantic and Pacific coasts of our country. It was 
easier to go sixteen thousand miles around Cape Horn than 
to traverse one thousand miles of mountainous surface. 

The effects of a lack of intercommunication are seen in the 
case of the Basques. More than two thousand years ago 
they were driven from the lowlands of Spain and France 
into the almost inaccessible valleys of the Pyrenees Moun- 
tains. During the succeeding years they have been so little 
in contact with the rest of the world that their language 
and customs have been changed but little. A similar 
effect is noticeable in settlements' of the Southern Ap- 
palachians. The rugged surface has shut them from the 
great lines of traffic ; the people have not materially changed 
their customs in a century of time. 

Intermontane valleys are usually productive. Their 
fertility cannot be easily impaired, because fresh soil is 
brought to them with every flood. As a rule, therefore, 
they are densely peopled. 

Passes have even greater importance than valleys. A 
mountain-range is an obstacle to communication, and the 
pass, therefore, is the channel toward which intercourse 
must be concentrated. Railway routes through mountain- 
ous regions are always surveyed and built through the 
passes. Almost every railway to the various commercial 
centres of the Atlantic seaboard seeks a way through the 
passes and water-gaps of the Appalachian Mountains. 

The wonderful development of New York City is due to 
Mohawk Gap, a pass that is the principal traffic route 



PLAINS, PLATEAUS, AND MOUNTAINS 83 

between the Great Lakes and the Atlantic seaboard. It 
is more nearly level than any other route across the Ap- 
palachian Mountains, and for this reason it furnishes a 
standard by which freight rates between the Atlantic sea- 
board and the Mississippi basin are regulated. 

Khaibar Pass, a narrow defile a few miles east of Kabul, 
for more than two thousand years has been a part of one 
of the great overland routes between Europe and India. 
Indeed, it is the chief gateway to India; and the truth of 
the old saying, "whoso would be master of India must 
first make himself Lord of Kabul," is every day more and 
more emphasized. 



QUESTIONS AND EXERCISES. — Name and classify the vertical 
forms in the State in which you live. On an outline map, shade or 
otherwise designate the areas of highland and lowland, using such 
contours, or lines of equal altitude, as may be available. If possible 
use the Relief Map of the United States noted below. 

Make a relief model in sand or paper pulp of any locality, the topog- 
raphy of which you know — State, county, township, or other region 
of interest. 

What results might occur were a mountain fold to be formed across 
the channel of a river? 

Make a sketch restoring the plateau or mesa dissected by weather- 
ing processes, as shown on p. 73. 

Name some of the benefits and the disadvantages resulting from the 
presence of the Appalachian Mountains between the industrial centres 
of the Atlantic coast and the Mississippi Valley. 

Explain why Fort Ticonderoga and Crown Point were important 
localities during the colonial wars. (Consult any good map of Lake 
Champlain.) 

On an outline map of each continent, or grand division, draw heavy 
lines representing the positions of the principal mountain-ranges. 

In what general drection does the rock waste of mountains move? 
Explain why. 

Give reasons why lowlands are more densely peopled than high- 
lands. 



84 PHYSICAL GEOGRAPHY 

COLLATERAL READING AND REFERENCE 

McGee. — The Piedmont Plateau. National Geographic Magazine, 
vii, 261. 

Willis. — Physiography of the United States, pp. 169-202. 

Hayes. — Physiography of the United States, pp. 305-336. 

Powell. — Exploration of Grand Canon, pp. 181-193. 

United States Geological Survey Maps, the following sheets: 
Tooele, Marion, Sierraville, Marysvillc, Kaihab, Fannerville, Spottsyl- 
vania, Mount Monadnock, Mount Mitchell, Huinmclstown, Relief Map 
of United States, and others. 



CHAPTER V 

DESTRUCTIVE MOVEMENTS OF THE ROCK ENVELOPE; 
VOLCANOES AND THEIR PHENOMENA 

Of the various phenomena that attend changes in the 
level of the rock envelope, two of them, volcanoes and 
earthquakes, are noteworthy because the results are more 




VESUVIUS, A TYPICAL CINDER CONE 

From a model. — Ajter Nasmyth. 

or less destructive. In the one case, great quantities of 
molten matter are ejected from fissures or vents, covering 
very large areas; in the other, there is a movement at 

85 N 



86 PHYSICAL GEOGRAPHY 

some part or other of the rock envelope, so sudden that a 
tremor, or even a severe shock, occurs. 

Volcanoes. — A channel or vent in the rock envelope 
from which steam and molten rock are ejected with great 
force constitutes a volcano. In most instances clots of half- 
molten rock fall about the vent and build up a conical pile. 
This is sometimes called a "volcano," but more properly, 
a cinder cone. At the top of the cinder cone is a cuj H-sha) led 
depression called the crater or, if very large, a coklera. 

The channel or tube is the essential part of the volcano, and the 
"mountain" or cinder cone, though rarely absent, is merely an incidental 
feature. 

The craters of the earth are small, compared with those of the moon. 
Terrestrial craters are rarely more than half a mile in diameter; lunar 
craters, on the contrary, frequently exceed twenty or thirty miles in 
diameter; Tycho and Copernicus are each more than forty miles. 
(See p. 12.) 

Volcanoes displaying energy are said to be active, 
quiescent, or inactive, according to the character of their 
energy. In a few instances the activity seems to be con- 
tinuous. Thus, the smaller cinder cones in the caldera of 
Mauna Loa are nearly always active, and Stromboli, " the 
Lighthouse of the Mediterranean," has been a mariner's 
beacon for more than two thousand years. Most active 
volcanoes, however, are intermittent in action; their erup- 
tions alternate with long periods of rest. 

Volcanoes in which all signs of activity have disappeared 
are said to be extinct. As a rule such volcanoes belong to 
previous geological ages. They are not easily distinguish- 
able. Usually the cone has been almost obliterated, nothing 
remaining except the masses of lava that are not easily 
affected by moisture and atmospheric elements. Mount 
Tom, Massachusetts, is an example of an old volcano. 



VOLCANOES AND THEIR PHENOMENA 87 




Phenomena of Eruption. — Most volcanic outbursts 
are similar: — that is, lava and steam are ejected from a 
vent or channel in the rock envelope. A volcanic eruption 
is therefore practically a steam explosion. Beyond this, 
however, the vari- 
ous types of erup- 
tion have but little 
in common. Fre- 
quently the eruption 
is preceded by earth- 
quakes, although 
these warnings are 
not always present. 
The explosion shat- 
ters the top of the 
cinder cone, the 
plug of hardened 
lava is blown out; 
most likely a new 
channel is formed 
on the one side or 
the other. 

The eruption of Vesuvius in 1756 took place, not at the former 
crater, but a little to one side of it. One of the old crater walls remained 
standing, and for many years was called Monte Summa. During the 
eruption of 1872 many vents were formed, and the flanks of the moun- 
tain were dotted with monticules. Professor Palmieri, who remained 
in his observatory on the mountain during the entire period of the 
eruption, said that the whole side of the cone "seemed to sweat fire 
at every pore." The eruption of 1906 did not greatly change the 
form of the cone. Since 1887, eruptions of iEtna, on the island of 
Sicily, have changed the form of the cone materially. 

In many instances the outrush of steam is mingled with 
mud and rock waste, and a cloud of inky blackness quickly 



ALTERATIONS IN THE SHAPE OF VESUVIUS 
' A.D. 63, 79 to 1631, 1767, 1822, 1868. 



88 



PHYSICAL GEOGRAPHY 




envelopes the cone. The condensing steam frequently 
produces heavy rains; and if sulphur gases are present, the 
rain may become so corrosive that vegetation is blighted 
and crops are destroyed. 

A flow of lava follows the outburst of steam. At first 
the lava is ejected with explosive violence. Later, the flow 
becomes steady and regular, behaving as though it were 
forced out by gases under high pressure. The clots of lava 
shot out of the crater sometimes contain so much steam as 

to burst explo- 
sively, flying into 
minute fragments 
when they strike 
the ground. Such 
clots are called 
volcanic bombs. 

The ejection of 
substances takes 
place, not only at the main vent, but also at new ones formed 
on the flanks of the old. At each vent small monticules, 
or parasitic cones, are formed, and the eruption from them 
does not differ from that at the main vent. 

The eruptions of some volcanoes are attended with no 
great violence, because the lava contains but little steam. 
Stromboli, a cinder cone of the Lipari Islands, is a notable 
example. From an overhanging crag of this volcano its 
eruption may be safely studied. At intervals of fifteen or 
twenty minutes gigantic bubbles form in the caldron of 
seething lava. In a few moments they rise to the top and 
bursting, hurl a shower of lava clots into the air. The 
phenomena are simply those exhibited by a viscous body 
in a state of slow boiling. In the case of Stromboli it has 



IDEAL SECTION OF A VOLCANO 

Minor eruptions are taking place through fissures in (he flanks 
of the cinder cone, building parasitic cones. 



VOLCANOES AND THEIR PHENOMENA 89 



been noted that when the barometer is low, the level of 
the lava is higher than at other times, and vice versa. 

The eruptions of the Hawaiian volcanoes are materially 
different from those of the Strombolian or the Vesuvian 
type. Instead of the -intermittent bubbles of Stromboli, or 
the violent outburst of Vesuvius, the lava rises in the caldera 
until it overflows the lowest part of the rim, or breaks 
through cracks and fissures in the ramparts of the caldera. 
The flow of lava — often an enormous quantity — continues 
for several days, or perhaps for several weeks, and then 
subsides as quietly as it began. 

Occasionally, clots of lava are shot into the air, and as soon as the 
ejected mass cools, the escaping steam or vapor blows the viscous lava 
into the fine, tenuous threads known as "Pele's hair." The threads 
are so gossamer-like that they are carried a long distance by the wind. 

Fissure Eruptions. — Some of the eruptions that oc- 
curred in previous geological periods resembled those of the 
Hawaiian vol- 
canoes. There 
were apparent- 
ly none of the 
phenomena that 
mark outbursts 
of the Vesuvian 
type. Great 
fissures were 
formed, through 
which the lava was forced. From some of these the flow 
of lava was enormous; in others the lava merely filled the 
fissure and hardening, left dykes of volcanic rock. The 
plains of the Columbia are the remnants of a lava flood 
from fissures in the Sierra Nevada Mountains. Large 




A LACCOLITE 

A section through Mount Hitters, one of the Henry Mountains. 
The dotted lines indicate the strata removed by erosion. 



90 PHYSICAL GEOGRAPHY 

areas of California, Oregon, Washington and Idaho were 
engulfed, and in several places the Columbia River was 
pushed out of its channel. Many small cinder cones were 
afterwards formed on the surface of the lava. In places, 
the sea of lava is nearly four thousand feet dec]), and the 
average depth is not far from one thousand feet. The area 
involved was not far from one hundred thousand square 
miles. The Palisades of the Hudson form a dyke of simi- 
lar character. In these sheets and dykes there is no evi- 
dence of explosive steam. 

The great lava floods came, not from craters, but from fissures. No 
crater in the world is large enough to have ejected a lava flood like that 
which covered so much of Oregon, Washington and Nevada. Calderas 
like those of Hawaii would have built up a dome-shaped mass of lava. 
The lava flood in question was a sheet. It could have come only from 
a fissure many miles in length. 

Small cinder cones represent volcanoes that formed on the lava flood 
after the surface had hardened. This fact indicates that vulcanisno 
occurs just as readily from a supramontane as a sxib-mountain reservoir. 

In many instances volcanic action has been nothing more than a 
mere filling of the fissure — an intrusion of lava, but no extrusion. In a 
few cases the upper edges of the fissure walls have been worn away, 
leaving the harder volcanic rock in the form of a ridge or dyke. The 
Devil's Slide, in Weber Canon, Utah, is an illustration. In this instance 
there are two dykes about twenty feet apart. 

Laccolites. — In a few instances, lava thrust upward, has 
raised the outer strata of the rock envelope in the same 
manner that a blister of the skin is formed. No extrusion 
of lava took place and none reached the surface. Irrup- 
tions of this kind are commonly known as laccolites. The 
Henry Mountains, a detached group of knolls in Utah, are 
examples. The Black Hills of South Dakota arc possibly 
a similar formation. 

Products of Eruption. — Excepting the small amount 



VOLCANOES AND THEIR PHENOMENA 91 

of sulphur gases emitted, but two substances are ejected 
from volcanoes — steam and lava. In the eruption of 
Vesuvius that occurred in 1872, it is estimated that ninety- 
eight per cent, of the material ejected consisted of steam. 
From the Hawaiian volcanoes, however, the matter thrown 
out consists almost wholly of great quantities of lava. 

The term lava includes every form of molten rock of 
volcanic origin. Lavas, therefore, differ not only in .ap- 
pearance, but in chemical composition as well. The spongy 
clots of lava, or scoria resemble furnace slag, and have 
much the same composition. If it contains much steam, 
it is vesicular, or spongy; pumice-stone, or "volcanic froth," 
is so porous that it floats on water. Obsidian, or "volcanic 
glass," another form, does not differ materially from black 
bottle-glass. 

Most lavas are readily decomposed by the action of air 
and moisture, and the Hawaiian lavas make excellent soil 
in the course of a few years. The economic value of lavas, 
therefore, may be considerable. Sulphur, or "brimstone," 
is a common mineral in and about the craters of volcanoes. 
It is formed by the action of sulphur gases that, on mixing, 
decompose each other and deposit the sulphur. ■ 

Nature of Volcanoes. — That volcanic action is due in- 
directly to the gradual shrinkage of the crust of the earth 
is generally admitted. To what extent contraction becomes 
a direct cause, however, is a matter of uncertainty. It is 
generally believed, also, that the material ejected comes, 
not from an assumed "liquid interior" of the earth, but is 
formed at a moderate depth below the seat of eruption. 

Various theories have been advanced to account for the 
possible causes of eruption, but of these only one or two 
are supported by positive evidence. When the rock layers 



92 



PHYSICAL GEOGRAPHY 



fit themselves about a shrinking interior, the pressure that 
results is sufficient to heat the rock upon it far beyond 
the temperature of fusion; and if a break or fracture oc- 
curs, the pressure being relieved, the superheated rock at 




JFR 



FORMS OF ERITTION 



A, a dyke; B, 23, subterranean intrusions; C, a cinder cone; D, a laccolitc; F, a lava sheet; 
G, granite core oj a range. 

once liquefies and is forced out of the fissure. An intrusion 
of water upon intensely heated matter may have caused 
such an eruption as that of Krakatoa, in Sunda Straits, 
but it is improbable that this is a cause of ordinary 
eruptions. 

There seems to be a relation between volcanic vents 
situated at no great distance from one another. Thus, 
while Vesuvius was dormant, Epomeo on the island of 
Ischia was active; but after the eruptions of Vesuvius began 
again, Epomeo became quiet. A similar condition existed 
in past times, for the Phlegrean Fields, an area south of 
Vesuvius, is honeycombed with old craters at which erup- 
tions took place at successive intervals. 

The same phenomenon is observed in the Hawaiian and 
the Ecuadorean groups. Activity is usually confined to a 
single caldera, and if this becomes dormant for any length 
of time the seat of activity is transferred to another vent. 
In the cases of the Italian and the Ecuadorean groups. 



VOLCANOES AND THEIR PHENOMENA 93 

the cessation of all activity is usually followed by a period 
of frequent and destructive earthquakes. 

A misunderstanding of volcanic phenomena has led to 
the adoption of certain names that often give erroneous 
ideas of volcanic action. There are no "flames" about 
volcanic outbursts; the so-called flames are merely the 
reflection of the white-hot lava from the under surface of 
the dense clouds of steam. 

This may be illustrated by a very familiar example. When a railway 
train passes through a long tunnel, a flood of mellow light illuminates 
the tunnel and the interior of the coaches. The light comes from the 
fire-box of the locomotive. When the furnace door is opened the light 
from the glowing coal is reflected by the steam that fills the tunnel. 
Each globule of water dust is a tiny mirror, and as a result the tunnel 
is flooded with light. 

"Smoke" is also absent, except as the clouds of dust and 
steam can be thus called. Volcanic "ashes" are not ashes 
at all; they consist merely of fine lava. This form of lava 
results from the action of steam which, forced through the 
lava by intense pressure, carries much of it along in a fine, 
powdery state. 

Results of Vulcanism. — Notwithstanding their stu- 
pendous display of energy, the physiographic effects of 
volcanic outbursts are comparatively unimportant, and as 
a rule they are confined to the vicinity of the volcano. 
The most noticeable feature is the cone, dome, or peak that 
popularly is called a volcano. Each volcano builds its own 
cone, and, for the greater part, the cones have been formed 
along the folds of mountain-ranges. 

The lava usually collects at the vents, and at the same 
time builds the cone higher. The successive eruptions of 
the calderas of Hawaii have formed a dome 14,000 feet 
high, covering an area as large as the State of Connecticut. 



94 



PHYSICAL GEOGRAPHY 



Most of the volcanic mountains of the Hawaiian Islands are 
dome-shaped rather than conical peaks. The shape results 
from the liquid condition of the lava and the absence of 
any great amount of steam. 

Some of the lava flows of the Iceland volcanoes have 
been extensive. Of the thirteen or more cinder cones, 
Hekla and Skaptar Jokul are the best known because of the 
frequency of their eruptions. In 1783, there occurred a 
flow 7 of lava from the latter that continued for two years. 




A SMALL CRATER WITHIN A CALDERA, HAWAIIAN ISLANDS 

Two streams each about fifty miles in length flowed in nearly opposite 
directions from the crater. More than 1,000 square miles were covered 
by the lava. A score of villages was swept out of existence. Streams 
were dammed by the lava and floods added to the destruction. Thou- 
sands of cattle were killed, and a large part of the population perished 
in the famine that resulted from the eruption. 

The ashes sometimes accomplish more ruin than the 
lava flow and the corrosive rain. Herculaneum and 



VOLCANOES AND THEIR PHENOMENA 95 

Pompeii were destroyed by the eruption of Vesuvius a.d. 
79. Pompeii was covered with loose material, and much 
of the city has been excavated in recent years. Hercu- 
laneum received a heavy fall of rain in addition to the ashes, 
and the latter were cemented into rock. 

Volcanic ashes have been hurled to a great distance by the wind. 
During the eruption of Tomboro, in Sunda Straits, dwellings forty miles 
distant were crushed and large areas of forests were destroyed. 

'. 

Appalling effects resulted from the eruption of Krakatoa, 
also in Sunda Straits. The explosions culminated with the 
disappearance of half of the island. Forests seventy-five 
miles away were crushed by the falling mud and rain, and 
the fine material covered the city of Bataviato a depth of 
several inches. Some of the lighter dust was carried more 
than 1,000 miles. 

Volcanic outbursts have occurred from time to time in the 
West Indies. Several eruptions have taken place in the 
cinder cone, La Souffriere. One in 1812 covered a large 
area with mud and ashes, destroying a town of ten thousand 
population; another in 1902 wrought great havoc in the 
cultivated region near by. An eruption of Mont Pelee, 
Martinique, in 1851, destroyed much property. A most 
disastrous outburst in 1902 wrecked the city of St. Pierre 
and killed about 25,000 people. 

Islands are both formed and destroyed by the outbursts 
of marine volcanoes. Off the coast of Tunis, a reef called 
Graham's Island was formed during an eruption, and re- 
mained in existence for several years. It then gradual- 
ly disappeared. The island of Santorini, in the Greek 
Archipelago, was formed as a result of eruptions. It is 
now inhabited. 



96 PHYSICAL GEOGRAPHY 

This island, better known as Thera, is a few miles north of Crete. 
According to one myth it grew from a clod of earth hurled from the 
ship Argo; according to another it was the product of submarine fires. 
Both legends are a testimony to its volcanic origin. The topography 
of the island was considerably altered by an eruption that occurred 
in 1866. The area covered by ashes and scoria is now cultivated 
land. 

Vulcanism is a trustworthy index of processes going on 
within the earth's crust which affect the level of a region. 
Measurements show that, in regions of volcanic activity, 
an elevation of the surface usually is taking place. Along 
much of the Mexican and South American coast, upheaval 
is occurring. In the South Pacific Ocean, on the contrary, 
where vulcanism seems to have ceased, there has been a 
subsidence. 

Distribution of Volcanoes. — Active volcanoes are com- 
monly found along the lines of the younger mountain folds. 
and they are almost always near the sea. The Pacific 
Ocean is nearly girdled by chains of mountains that are 
comparatively young, and in these folds are situated a 
majority of the active and dormant volcanoes of the earth. 

Another short chain extends along Java and the re- 
maining Sunda Islands to New Zealand. It contains 
about one hundred active and dormant volcanoes, and is 
the chief seat of volcanic activity on the earth. The Ha- 
waiian Islands are the most notable group situated in mid- 
ocean. This chain is about a thousand miles long, bul the 
seat of activity is confined mainly to the island of Hawaii, 
on which there are three calderas — Kea, Loa, and Kilauea. 

A chain of volcanic islands extends along the Atlantic 
Ocean from Jan Mayen Island through Iceland, the Azores. 
Canary, and Cape Verd Islands, southward as far as Tristan 
da Cunha. Another extends through the West Indies. 



VOLCANOES AND THEIR PHENOMENA 97 

Graham Land, in the Antarctic Continent, contains at 
least two volcanoes that have been active in recent times. 

Among South American volcanoes the Peruvian and 
Ecuadorean groups are famous for their great height. The 
Mexican group contains four of interest, because they are 
so far inland. In what direction does the line extend? 
They are active or quiescent at short intervals. 

The North American group contains a great many 
dormant and extinct cones; but at least four — Shasta, Ta- 
coma (or Rainier), and Lassen must have been active within 
recent times. A small cone near Lassen Peak has been in 
eruption probably within seventy-five years, and the 
stumps of trees, many of them in a good state of preserva- 
tion, are still protruding through the sheet of lava. 

Cinder cones and volcanic "necks" are abundant all 
through the plateaus of the Western Highlands. In Ari- 
zona there are several hundred. One of the most imposing, 
San Francisco Peak, has been in eruption within recent 
times. In New Mexico there are also many small cones. 
Almost all the high peaks of the Cascade and Sierra Ne- 
vada Ranges are cinder cones. 

The Aleutian group contains about thirty cones, quies- 
cent and active. One of these, Bogoslov, north of Una- 
laska, has been in eruption almost constantly since 1880. 
Many of the peaks of the West Indies are cinder cones. 
The remains of old cones are abundant in the Appalachian 
and Laurentian Mountains, but they seem to have long been 
extinct since early geological times. One of them, Mount 
Royal, has given to the city of Montreal its name. 

QUESTIONS AND EXERCISES.— Explain the nature of the so- 
called smoke, flames, and ashes of volcanic eruptions. Why are these 
terms inapplicable? 



98 PHYSICAL GEOGRAPHY 

Prepare a written description of the geographic distribution of 
volcanoes, taking into consideration their position with reference to 
mountain-ranges, proximity to the sea, latitude, and situation with 
reference to continents and islands. Consult the map on the oppo- 
site page. 

Note the features in the diagram, p. 92, and prepare a brief descrip- 
tion of the various ways in which lava is extruded. 

COLLATERAL READING AND REFERENCE 

Pliny. — Letters — Book vi., 16 — vi. 20. 
Shalek. — Aspects of the Earth, pp. 46-97. 

" First Book of Geology, pp. 88-97. 

Le Conte. — Elements of Geology, pp. 89-103. 
Redway and Hinman. — Natural Advanced Geography, p. 12. 
United States Geological Survey. — Shasta and Lassen sheets. 



1 <f 




i. we. 



CHAPTER VI 

DESTRUCTIVE MOVEMENTS OF THE ROCK ENVELOP]-:: 
EARTHQUAKES 

Rigid and solid as it seems, the rock envelope is elastic. 
This is noticeable when an underground explosion occurs, 
or even when a very heavy weight falls to the ground the 
latter trembles for an instant, causing a slight shock. 

The explosion under Flood Rock, for the purpose of widening Hell 
Gate Channel, produced an earth shock that did not differ from those 
produced by natural causes. The earth shock resulting from this ex- 
plosion was recorded at a distance of forty miles from Hell Gate. The 
velocity of the wave varied from 5,000 to 8,000 feet per second in the 
vicinity of the explosion. 

Any instantaneous disturbance, therefore, such as a sub- 
terranean explosion, the collapse of a cavernous space, or 




THE PROGRESSION OF EARTHQUAKE WAVES 

the sudden breaking of strata, causes a vibration or trem- 
bling of the surrounding rock. These tremors are earth- 
quakes. They may be perceptible for several seconds, or 

loo 



EARTHQUAKES 101 

even a minute. Usually several shocks follow at brief 
intervals, involving an area of many square miles. 

Nature of Earthquakes. — No matter how far below 
the surface of the rock envelope the centre of the disturb- 
ance may be, as soon as the vibrations reach the surface 
they behave like the circular waves that form when a 
stone is thrown into still water. 

The vibrations as they form underground are spherical waves and 
much like those formed in the air by the discharge of a firearm or the 
ringing of a bell. When the waves reach the surface of the rock envelope 
they spread out in the form of circular waves. 

In the diagram on page 100 the shock originates at O, 
and immediate^ above, the resulting wave will have an 
up-and-down motion. These are called vertical waves. 
As the successive waves move outward, the 'vertical move- 
ment gives place to one that is both horizontal and progres- 
sive, and the latter may be called a horizontally progressive 
wave. At F the waves are nearly horizontal; at B and C 
they partake both of the vertical and the progressive 
character. 

Researches, however, indicate that the tremors or vibra- 
tions do not always spread out so evenly from the centre 
of disturbance as the waves that result when a stone is 
thrown into water. Some kinds of rock seem more elastic 
than others, and so the concentric waves, instead of re- 
maining circular in form, become irregular in shape. If the 
waves of water strike a rigid surface, they are reflected, the 
reflected 'wave often crossing the original. Earth waves 
are similarly reflected, and sometimes they produce the 
effects of a vorticose, or whirling movement. 

Such waves have a terrific shattering force; but those in which the 
horizontal and vertical components are combined are even more destruc- 



102 PHYSICAL GEOGRAPHY 

tive; they not only shatter, but they produce a rocking motion as well. 
Vertical vibrations may only shatter a building; a "roller" will not only 
shatter, but overthrow it. 

Although earthquake waves are similar to the circular 
waves formed at the surface of water, it must be remembered 
that they differ greatly in velocity and energy. The latter 
progress only a few yards a minute; the former have a 
velocity of more than forty miles a minute. 

It has been calculated that the amplitude, or up-and-down motion, 
rarely exceeds one-quarter of an inch in height; and ordinarily, in 
severe shocks, it is seldom more than one-twentieth of an inch. The 
horizontal oscillation is scarcely more than half an inch, and even when 
it is less than half as much, the shock has great shattering power. 

The velocity of the wave depends partly on the elasticity 
of the material through which it travels, and partly on the 
energy with which it is propagated. In hard, crystalline 
rock it travels rapidly and extends a great distance: in 
sand and loosely coherent rock the velocity is much slower, 
for the waves quickly lose their energy, but they are even 
more destructive than those passing through rock. 

During the earthquake at Riobamba, Ecuador, the vertical movement 
was sufficient to hurl heavy objects a hundred feet into the air. The 
bodies of men were thrown several hundred feet across the river. 

In severe earthquakes a series of shocks follows one 
after another with increasing intervals of time. The first 
shocks are commonly the most violent. The duration of 
the shock is not perceptible to the senses for more than four 
or five seconds, but careful measurements by the seismo- 
graph, an instrument for the detection of shocks, show that 
it may last for more than a minute. 

At St. Thomas, one of the Lesser Antilles, there were nearly three 
hundred shocks during the earthquake of 1868. The earthquakes that 



EARTHQUAKES 



103 



shatteied San Salvador, the capital of the State of Salvador, lasted for 
about ten days. The Charleston earthquakes did not cease for nearly 
a month, and a hundred similar instances might also be added. All 
this accords with the well-known law that a mass of rock envelope, in 
changing its foundations, 
cannot adapt itself to its 
new position at once, but 
does so gradually. 



The focus of the 
shock may vary 
from a short dis- 
tance to several 
miles below the sur- 
face of the earth. 
The area involved in 
the earth- waves may 
be either circular or 
elliptical. The di- 
ameter of the area 
seldom exceeds one 
thousand miles. 



The elliptical form is 
especially noticeable in 
mountain regions, and 
the major axis, or long 
diameter of the ellipse, 
coincides with the trend 
of the range or system. 
The reason is that the strata of rock are more elastic along than across 
their masses. 

Attending Phenomena. — Earthquakes are frequently 
attended by sounds — sometimes like low, rumbling thunder ; 
very commonly, however, the noise is like that of a heavily 
loaded wagon going rapidly clown a gravelled incline. 




A ROCK COLUMN LIKELY TO BE OVER- 
TURNED BY AN EARTHQUAKE 

The rock has broken away from the cliff, splitting along a 
naturally formed plane. Rock waste, jailing into the 
crevice, has become saturated with water, which by freez- 
ing, has expanded and pushed the mass farther and 
farther from the cliff. 



104 PHYSICAL GEOGRAPHY 

In the great majority of earthquakes the effects are 
not severe; they rarely extend beyond the stopping of 
clock pendulums, the swinging of chandeliers, or the break- 
ing of delicate substances. In severe shocks the walls of 
houses are wrenched and cracked, and the ground is fissured. 
In disastrous shocks buildings are shattered and the surface 
of the earth is seamed with deep fissures and chasms. 
Lakes have even been formed or, perhaps drained, and 
stream channels are sometimes changed. 

The earthquake that destroyed the city of San Salvador broke down 
the rim of a small lake and drained it. The famous earthquake of New 
Madrid, Missouri, changed the level of the land to such an extent that a 
permanent swamp was formed at a locality that before the shock was 
high and dry. Tins area has since been known as the "Sunk Region." 
During this shock the current of the Mississippi was greatly disturbed 
as was shown by changes in its channel. Reelfoot Lake, in Tennessee, 
was considerably enlarged at the same time. 

If the centre of the shock is in or near the ocean it is 
commonly followed by a series of gigantic waves, popularly 
but incorrectly called " tidal" waves. Following the Lisbon 
earthquake in 1755, enormous waves rolled in from the sea, 
and wrecked whatever the earthquake had left, The ocean- 
waves that followed the earthquake at Arica, Peru, carried 
the United States Steamship Wateree nearly seven miles 
inland, leaving her stranded in a dry stream bed. 

Probably the most disastrous waves on record, however, followed the 
Lisbon earthquake. After the town had been felled by shocks so terrific 
that thirty thousand people perished, most of the survivors took refuge 
on the massive sea-wall. Hardly had they reached it when the water 
began to recede, leaving the harbor dry. Then an enormous wave, 
sixty feet high, rolled in and completed the destruction, and thirty 
thousand more lives were swept out of existence before the waves ceased. 
At Cadiz the waves were thirty feet high, at Madeira eighteen, and along 
the Irish coast they were four or five feel in height. 



EARTHQUAKES 



105 



The sea-wave resulting from earthquake at Arica crossed the Pacific 
Ocean and was recorded at Yokohama, Japan, twenty hours afterward. 
On the American coast the wave was observed as far north as Alaska, 
and to the westward as far as Australia. The earthquake that in 1854 
devastated a part of Japan was followed by a destructive wave. At 
Simoda the wave was thirty feet high; at Peel's Island, one thousand 
miles away, it was fifteen feet ; on the California coast it was from twelve 
to eighteen inches in height. 




AN EFFECT OF THE EARTHQUAKE AT CHARLESTON 
The crack was about two jeet wide; it is a definite fault. From a photograph. 

Cause of Earthquakes. — It is generally believed that 
earthquakes are the result of the movements of the rock 
envelope. If the strata slowly adjust themselves, no vi- 
bratory effect is noticeable, but if the strain increases until 
a fracture, or a collapse takes place, the shock produces 
the vibrations that constitute the earthquake. 

When fissures are formed, one wall usually slips upon the 
other, so that the two edges are no longer in the same 



106 



PHYSICAL GEOGRAPHY 



level. The resulting inequality is called a fault, and 
wherever such fault ings are found, they indicate, if not 
an earthquake, at least a surface disturbance. The ex- 
istence of such faults, therefore, is evidence that the outer 
shell of the earth is constantly under stress, and that the 
release of the strain produces the earthquake. 

The investigation of the San Francisco earthquake has 
made this fact quite clear. Several faults extend along the 
ridge of the Coast Range next the Pacific Ocean. The 
shock of April, 1906, resulted from a movement along the 
line of the San Andreas fault. The vertical displacement 

along the fault scarcely 
exceeded four or five 
feet at any place: for 
the greater part it was 
hardly more than one 
foot. The lateral dis- 
placement in several 
places was about sixteen 
feet. This is illustrate! I 
in the accompanying diagram and photograph (p. 107). 
At this point the lateral movement pulled the fence out 
of line about six feet. 

The destruction of Babispe, a small village in northern Mexico, is 
also an excellent illustration. The shocks made a fissure extending 
several miles in length; when equilibrium was restored, the fissure had 
become a fault — one wall being from ten to fifteen feet lower than the 
other. 

The rock in the large quarries usually exhibits signs of heavy strain. 
At Monson, Massachusetts, Professor Niles observed that pieces, before 
their ends had been detached, were split along a horizontal plane and 
bent upward at the middle. One mass, measuring 354 X 1 1 X -i feet, 
increased an inch and one-half in length after it had been detached. 
These facts indicate the enormous pressure to which rocks may be sub- 




SAN FRANCISCO EARTHQUAKE: 
LATERAL DISPLACEMENT 

AB, the position of the blocks before the shock; 
A'B', the position after the shock. 



EARTHQUAKES 



107 



jected; incidentally they show that even the hardest rocks are decidedly 
elastic. 

Distribution and Occurrence of Earthquakes. — No 

part of the earth is free from earthquakes, and recent 
observations have shown that, somewhere or other, they 




LATERAL DISPLACEMENT, SAN FRANCISCO EARTHQUAKE 
From a photograph by C. T. Wright, Redlands, Col. 

are of almost daily occurrence. As a rule, they are so 
feeble that scarcely one in fifty is perceptible, without the 
aid of instrumental measurements. 

An instrument for measuring any of the elements of an earthquake 
shock is called a seismometer; if it merely records a shock it is a seis- 
mograph. The horizontal element of the shock is recorded by means 
of a delicate pendulum carrying a pencil or stylus. The jar sets the 
pendulum in vibration, and the pencil records the direction of the 
oscillations. 



108 PHYSICAL GEOGRAPHY 

Earthquakes are more frequent in younger mountain- 
ranges than in the older ones. They are still less frequent 
in plains, unless the latter are undergoing a process of up- 
lift or depression. They also accompany most volcanic 
disturbances, and the sudden formation or the rapid motion 
of gases will account for the shocks at such times. Volcanic 
earthquakes do not differ in effect from others; they arc 
due merely to a different cause. 

The study of several thousand earthquakes shows thai 
shocks are a little more frequent when the earth is nearest 
the sun, and that they are also more prevalent when the 
moon is nearest the earth. An explanation for this is 
not hard to find. Owing to the tendency to adjust itself, 
the rock envelope is constantly under an increasing stress. 
But when the earth approaches either the sun or the moon, 
the increased mutual attraction adds its force to the strain, 
and a shock results. 

Of a total of 364 shocks in the United States, 147 occurred in the 
Atlantic Highlands and Coast Plain; 66 in the Great Central Plain; 
and 151 in the Pacific Highlands. These figures have only an approxi- 
mate value, however, inasmuch as many of the earth shocks occurring in 
the sparsely settled regions of the Pacific Highlands escape notice ( >f 
66 shocks recorded in Canada, the United States and the West Indies 
during one year, 24 were in the Atlantic slope and the West Indies; 3 
were in the Great Central Plain; and 39 in the Pacific Highlands, in- 
cluding Mexico and Central America. 

QUESTIONS AND EXERCISES.^If you live in the vicinity of a 
body of water, study the waves that form when a good-sized stone is 
tossed so that it falls vertically into still water. 

What is the relative position of the vertical and the horizontal. > 
progressive waves? Repeat the experiment until the results obtained 
are familiar. 

If possible, clamp a brass or metal plate, about a foot square, to a 
firm table, so that the clamp holds the plate at its centre. Sprinkle dry 



EARTHQUAKES 109 

sand on the plate and draw a violin bow across the edge. From the 
figures produced by the sand note the direction and character of the 
vibrations. 

COLLATERAL READING AND REFERENCE 

Rockwood. — Notes on American Earthquakes. 

Shaler. — Aspects of the Earth, pp. 1-45. 

Le Conte. — Elements of Geology, pp. 154-171. 



CHAPTER VII 

THE WASTING OF THE LAND: THE WORK OF RIVERS 

While internal forces result in wrinkling and folding 
the strata of the rock envelope, other agents are constantly 
at work wearing away those same folds and irregularities, 
and are wasting or degrading the surface of the land to its 
lowest, or base level. 

Weathering Processes. — Water in its various forms is 
the chief agent in the wasting and changing of the earth's 
surface. Falling on the land as rain, it loosens and carries 
off particles of earth. It also sinks into the pores of the 
rock, perhaps dissolving some of it or else breaking off small 
pieces. This process of degradation is called erosion. 
Gathering in swift torrents, the waters cut their channels 
deep into the surface, producing the effects called cor- 
rosion. Flowing against cliffs and banks, it saps their 
foundations and breaks them down by undermining. 

Gravitation aids in the process of degradation, for not 
only does the water flow downward, but the detritus, or 
rock waste, is likewise moving -to lower levels. For a time 
it may lodge in a hollow, or basin-shaped depression, until 
the latter is filled; then the downward progress again begins. 

Disposition of Storm Waters. — An average of about 
three feet of water falls on the land each year. In regions of 
ordinary rainfall, some of the water evaporates and mingles 
with the air; a part sinks into the ground and fills up the 
underground channels; the remainder flows back to the sea. 

ill 



112 PHYSICAL GEOGRAPHY 

Streams of water flowing upon the land are variously 
called rills, rivulets, brooks, creeks, and rivers — the name 
usually depending on the size of the stream. The largest 
streams are rivers. Almost every river is made up of 
branches and tributaries, and these, in turn, are fed by 
smaller branches. A stream with all its branches is called 
a river system. The area drained by the river system is its 
watershed or basin, which is partly surrounded by a ridge or 
divide, that separates it from adjacent basins. 

The term "watershed" is often used as a synonym of "divide." 
Technically used, however, it is not a divide but a basin. 

Sometimes the crest of a mountain-range forms a divide, 
but occasionally the latter is an almost imperceptible rise 
of ground only a few feet high. Thus, at Chicago, the 
divide between Lake Michigan and a tributary of Illinois 
River is only ten or fifteen feet higher than the level of the 
lake. There are instances, also, in which the divide is so 
ill-defined that the same pond or lake may discharge its 
waters into streams whose mouths are a great distance apart. 
At high-water, Two-ocean Pond, in Yellowstone National 
Park, has two outlets — one through the Yellowstone to 
the Mississippi, the other through the Columbia. The one 
has Atlantic drainage; the other flows into the Pacific 
Ocean. 

In some instances, too, the land is so flat that the drainage is difficult 
to determine. Such is the case of the Cassiquiare, a South American 
stream. In its course it bifurcates, discharging simultaneously into 
the Orinoco and the Rio Negro, the latter a tributary of the Amazon. 
Between the headwaters of the Parana, and those of the southern 
tributaries of the Amazon, the land is so flat that, in places, the drainage 
is undecided. 

A high mountain-range is not necessarily a divide, for 
there are many instances where ranges are crossed by rivers. 



THE WASTING OF THE LAND : RIVERS 113 

From any good map find the divide between the Susque- 
hanna and Allegheny Rivers; between the Great Kanawha 
and Ohio Rivers. Compare the divides with the ranges. 

Physiography of Rivers. — The beginnings of most 
large rivers are in the mountains, where the rainfall is 
heavy and the greatest accumulation of snow is found. The 
water let loose from a spring or from a winter's snowdrift 
trickles down the slope in tiny rills. On their way the rills 
unite into streams that tumble down the mountain- slopes 
in self-made gorges. Soon they become mountain torrents 
that rush down the steep inclines, cutting channels into 
hard rock and tossing to the one side or the other the 
obstacles in the way. Almost always the mountain torrent 
flows in a deep canon. 

The cutting and the carrying power of water depends on the speed of 
the current. A slight difference in the velocity makes a great difference 
in its carrying power. Water flowing at the rate of four miles an hour 
will carry sixty-four times as much material as water flowing at half that 
rate of speed; that is, the carrying power varies inversely as the sixth 
power of the velocity. 

When the stream emerges from the canon it is burdened 
with rock waste brought from the mountain side. No 
longer able to carry all of the rock waste, because of the 
lessened slope of its bed, it drops the coarser material, 
which forms a fan-shaped pile, or alluvial cone. Thence- 
forth, because its current is slower, it cannot remove the 
heavier obstacles in its way, but must flow around them. 

The lighter rock waste, called silt, or sediment, is still 
carried by the flood of the river. Some of it is dropped, 
being built into flood plains, but the lightest material 
is borne to the coast plain, which itself is the "made- 
land" formed of river sediments. When the river reaches 



114 



PHYSICAL GEOGRAPHY 



tide-water, most of the remaining sediment is deposited — 
either to be spread out in the form of a delta, or to be 
piled up near the shore in spits and bars. 

As a stream degrades, or wears away the land, throe 
processes are usually going on, namely — corrasion and 
undermining, transportation, and deposition. From the 

moment the water 
falls on the rock 
envelope it is pick- 
ing up particles of 
earth; it is carry- 
ing them; or else 
is dropping them. 
Whichever it does, 
depends on the ve- 
locity of the cur- 
rent. Increase the 
velocity, and the 
water will pick up 
more particles; de- 
crease it, and the 
water will d r o p 
and flow around 
them. In the up- 
per, or torrential 
part, streams usu- 
ally cut their chan- 
nels deeper. In the lower course the reverse is apt to be 
true; the stream clogs its channel with sediment and must 
therefore make a new one around the obstruction. 

In the study of such rivers as the Mississippi, the reasons 
for this are not hard to find. Because the slope of its 




LOOPS AND CUT-OFFS OF THE LOWER MIS- 
SISSIPPI 

The abandoned channels jorm an intricate network oj pas- 
sages. 



THE WASTING OF THE LAND: RIVERS 115 

channel decreases, the velocity of the current is checked, 
and because of the slackening current, the water is con- 
stantly dropping sediment. 

Islands are common in rivers carrying a considerable 
sediment. The anchoring of a snag, or any other obstacle, 
slackens the current and causes deposition of sediment. 
The latter increases in amount until finally it reaches the 




ISLANDS IN THE MISSISSIPPI RIVER 



surface. Then vegetation takes root and an island results. 
Drifting timber may clog the channel. The roots of a 
floating tree catch on the bottom, forming a snag. Other 
timber lodge upon it, and in time form a "raft." Per- 
haps the latter may float down stream, but more likely 
it forms a permanent obstruction. The famous Red River 
raft is many miles in extent. 



116 



PHYSICAL GEOGRAPHY 



The Formation of Loops. — The river which flows over 
a decreasing slope has a tendency to form loops or, "ox- 
bows," in its lower course. In general, such loops arc long 
lived, but if there is a succession of years of high water, 
the conditions are changed. The volume of water is in- 
creased, the current is quickened, and the water begins to 
pick up the sediment which it had dropped. In time, the 

neck of the loop is cut away, 
and the river shortens its 
channel — sometimes by 
twenty or thirty miles. The 
line of moats, or oxbow lakes, 
along the lower Mississippi 
marks the old loops and 
abandoned channels along 
this river. It is evident also 
that the great amount of 
sediment removed when a 
loop is destroyed must be 
carried farther down stream 
and there deposited. New 
bars were formed at various places below the cut-off, and 
the navigable channel was materially changed. 

Davis cut-off at Palmyra Bend, near Vicksburg, Mississippi, is the 
channel across the narrow neck of an oxbow. The distance around the 
loop was twenty- two miles; across the neck, it was scarcely half a mile. 
An obstruction anchoring in mid-channel forced the current against 
the narrow neck, and the latter was cut away by the stream. Finally 
the neck was severed and the river poured through the cut. Around the 
loop the fall of the river was about four inches per mile; through the 
cut it was more than five feet. The river scoured a channel about one 
hundred feet in depth; and so swift was the current that more than a 
week elapsed before steamboats could ascend it. The effect of the 
cut-off was far-reaching, and extended both above and below Palmyra 




PALMYRA BEND— NOW PALMYRA 
LAKE 



THE WASTING OF THE LAND: RIVERS 117 

Bend a distance of over one hundred miles. More than a year elapsed 
before the changes in the channel ceased. 

Growth and Development of Rivers.— A river and 
its basin are not an unchang- 
ing feature of the land. On 
the contrary, a river passes the legitimate work of a 
through the various stages river 

p • c -i , • , . , It removes the rock waste from A and car- 

oi mlancy and maturity; its He* u toward b.- a b, the ou-, a! v, the 

legitimate work is to carve 

away and remove the material of its basin until every 

part is worn down to a base level. 

The moment that a plain or surface — such, for instance, 

as the coast plain of New Jersey — is uplifted and exposed 

to the action of the weather, the water falling upon it 

begins to gather and to form 

channels. Such a river may 

. infant stage of a river 

be called an mlant stream. The stream has nolched its channd in ihe 

plain A B. 
It is also called a consequent river 
because its formation is consequent upon the elevation of the plain. 
A river is an antecedent stream when its existence dates before that 
of some other feature. Thus Green River existed before the formation 
of the Uinta Mountains and with respect to them is an antecedent 
river. 

A young stream at first drains its basin very imperfectly. 
It encounters many obsta- 
cles; and if the slope is gentle, 
it finds great difficulty in TRE MAT(JRE STAGE QF A RIVER 

making a Channel. .Because The main stream and its tributaries have 

n . i • -i . , . • carved deep channels in the plain A B: In 

OI the many inequalities m a! V c' the remaining material has been 

., r . , . carried away. 

the surface, lakes and swamps 

form in the slight depressions. The channels are apt to be 

shallow and the divides between the adjacent branches are 



118 PHYSICAL GEOGRAPHY 

neither permanent nor well defined. In consequence, any 
unusual flood may result in the abandonment of an old and 
the selection of a new channel. Red River of the North 
is an example of an infant river. 

As a stream reaches maturity its character is changed. 
The channel is deepened and is more permanent. The 




YOUNG RIVERS 

The stream on the right has uncovered the ledges of hard rock shown in tlte margin, and jails 

have resulted. 

gullies of the tributary streams are deepened into ravines, 
or, possibly, are sculptured into broad valleys. The tribu- 
taries extend their channels backward and often capture the 
waters of other streams less vigorous (p. 119). The mature 
stage is the age of its greatest vigor and power. It may 
lengthen itself by forming a delta at its mouth, and it may 
also cut its headwater channels backward. 



THE WASTING OF THE LAND: RIVERS 119 



The old age begins when the river has cut away and 
transported all the available material within the reach of 
its various branches. As a matter of fact, however, a 
stream rarely ever reaches old age. Changes in the eleva- 
tion of its basin are constantly taking place. A slight 
elevation of the basin or some part of it, or an increase in 
the volume of water, may rejuvenate the stream. Just 




A GROUP OF MATURE RIVERS 

The greater part of the basin of each has been removed. The tributary of the central 
stream is carving its way into the basin of the river on the right and -will eventually absorb the 
headwaters of the latter. 

as a log moved against the saw results in cutting the tim- 
ber, so a gradual uplift of the stream channel gives to the 
river youth and fresh cutting power. An increase in the 
volume quickens the current and -also increases its cutting 
power. Uplift is nearly always followed by extensive 
stream corrasion. 

Flood-Plains. — In its mature age a stream removes 
more material from the upper or torrential part than it can 
carry. Just as soon as the slope decreases, the current 



120 PHYSICAL GEOGRAPHY 

is checked and sediment begins to be dropped. Much of 
this is spread along the sides of the stream, thereby forming 
the "bottom lands" or flood-plain. 

In its infant stage the river has but little cutting power 
and usually can carry all the material it removes. When 
the headwater streams acquire greater vigor, however, 
formation of the flood-plain begins. 

The deposition Of sediment is constantly going on. The 
river may build its bed and banks a little higher than the 
level on either side, continuing the process until the coming 
of high water; then it breaks through its banks and makes 
a new channel in lower land. 




SECTION SHOWING A FLOOD-PLAIN 

The dark shading represents the sediment deposited by floods. 

The Destruction of the Flood-Plain; Terraces. — 

After a river has cleared away the rock waste at head- 
waters, it may then attack its flood-plain. Instead of de- 
positing sediment, on the flood-plain the water begins to 
remove it. Then it forms a deeper channel, along the sides 
of which a new and lower flood-plain is formed. The new 
flood-plain with the remnant of the old one form terraces. 
Of these there may be several. 

Flood-plains and terraces are, therefore, incidents in the 
history of a river. Perhaps most of the rivers of the United 
States are in the flood-plain stage of their existence. Some 
of the streams of the northeastern part arc in the terrace 
stage and arc approaching the period of old age. 



THE WASTING OF THE LAND: RIVERS 121 



Deltas.— Salt water has a remarkable effect in clearing 
muddy, fresh water, and the moment the two mix, the 
sediment held in suspension is deposited. Unless the sedi- 
ment is swept away by currents and tides, a considerable 
accumulation will form at the mouth of the river. 

The mouth of the Mississippi River shows an interesting 
type of delta formation. In this case it is evident that the 
banks of the delta are self-made, and they have been formed 
because the current has been checked more effectually at 
the edges than in mid-stream: Since the lower Mississippi 
has occupied its present channel, the river has extended its 




TERRACES IN A FLOOD-PLAIN 

Each marks a stage of down-cutting. The darker shading shows the old bed of the river. 

lower part about one hundred miles into the Gulf of Mexico. 

The deltas of the Volga, and Ganges-Brahmaputra are 
older and more complex than that of the Mississippi. They 
are also more compactly filled with sediment. The delta 
of the Ganges-Brahmaputra is perhaps the most extensive 
known. Its frontage on the Indian Ocean is about two 
hundred miles, and its area is greater than that of Texas. 
Much of the land consists of shifting mud-flats, and the 
whole region is subject to destructive inundations. 

The delta of the Adige-Po has developed in a manner not 
unlike that of the Ganges. Probably no other river of its 



122 



PHYSICAL GEOGRAPHY 



size brings down more sediment than the Po. As a result, 
its delta isjSlling and extending so rapidly that the town of 
Adria, in Julius Cicsar's time a seaport, is now more than 
twenty miles inland. Ostia, once at the mouth of the 
Tiber, is now about seven miles inland. 

Delta lands surpass almost all others in productivity. 




A DELTA MOUTH: THE DELTA OF THE MISSISSIPPI RIVER 



The soil is very rich, and, because of the constant additions 
from the river, it is enriched as fast as it is impoverished. 
The Nile delta has long been known as the granary of 
Egypt — the delta lands of the Ganges-Brahmaputra are 
among the foremost rice-producing fields of the world. 

Estuaries. — While some rivers reach the sea through 
deltas, others with equal power flow into estuaries. The 



THE WASTING OF THE LAND : RIVERS 123 



Mississippi and the Delaware are contrasting examples. 
In the former case the river has a tendency to block its 
mouth with sediment; in the latter, a downward movement, 
or sinking of the coast, has practically drowned the mouth 
of the river. Moreover, between its tide-formed bars, the 
tidal current is usually strong 
enough to keep the channel 
clear. So, between the scour- 
ing action of the tide and the 
sinking of the valley, there is 
a broad and a deep area of 
water in most estuaries. If 
the mouth of the river is in a 
coast plain, the estuary usually 
takes a form much like that of 
Delaware Bay. Along a rugged 
coast, however, the estuaries 
are more-like, the indentations 
of the Maine coast. Along the 
coast of Norway they are called 

fjords. CHESAPEAKE BAY: AN ESTUARY, 

OR "DROWNED" RIVER- MOUTH 

The lower part of the Hudson A p art } a comparatively level plain has 
River is a drowned valley in which subsided below sea-level. 

many characteristics of the fjord are 

observable. The real mouth of the Hudson is near Troy. Below this 
point the river is an arm of the sea, swept by tides. The explorations 
of the United States Coast Survey have disclosed the old channel of the 
river which extended southeast from lower New York Bay, a distance 
of eighty miles. Were this part of Atlantic coast again to be raised, 
it is not unlikely that the river would recover its long-buried channel. 

The sediment of rivers that flow into estuaries is de- 
posited in the form of bars. In most instances two bars 
are formed, one at the mouth, the other at the head of the 




rvvL V), 



124 PHYSICAL GEOGRAPHY 

estuary. The double deposition of sediment is due to the 
tides. Bars are formed in comparatively still water, so, 
when the tide is slack at flood, the deposition takes place at 
the head of the estuary; when it is slack at ebb, the deposi- 
tion forms the bar at the lower end. 

The estuary favors commerce and navigation, while the 




A FJORD MOUTH OF A RIVER 
Its situation adapts it for the centre oj commerce of a newly-settled region. 

delta is a hindrance. The navigable channel of the Mis- 
sissippi delta has been kept open at an enormous expense. 
All the great commercial seaports are on the shores of 

estuaries. 

In many instances the water of a small stream reaches the sea in- 
directly. This happens when the force of the sea is greater than that 
of the river. Its mouth may he blocked by bars, and the stream La 
compelled to make a new one as it flows alone; the coast to find a 
place where its current has force enough to keep a clear outlet; or the 
mouth may be completely blocked so that thi- water gets to the sea by 



THE WASTING OF THE LAND: RIVERS 125 

percolating the sand. Some of the streams flowing into Lake Michigan 
are imperfectly, others pre completely blocked. Blocked rivers and 
" bottle " estuaries are common on the west coast of the Atlantic States. 

Cascades and Rapids. — In flowing to lower levels, if 
the slope is abrupt, the water descends in rapids to com- 
paratively level reaches. The river bed is therefore more 
or less terraced. The streams of the New England Plateau, 
and the torrents of mountainous regions are illustrations. 
In some instances, however, the stream plunges over a 
vertical embankment in the form of a cascade or fall. 
Of these, Niagara Falls, Spokane Falls, and those of the 
Zambesi River are illustrations. Some mountain streams 
make tremendous leaps. In the Yosemite Valley, Merced 
River falls 2,600 feet in three plunges; and Bridal Veil Fall, 
with a sheer pitch of 1,500 feet, reaches the lower level in 
the form of fine water dust. The Staubbach ("brook 
dust") of the Alps is a similar cascade, having a fall of 900 
feet. The Cascade Range of the United States and the 
Lauterbrunnen ("nothing but fountains") of the Alps are 
names that suggest the character of these regions. 

Sometimes the stream has little to do with making the 
cliffs over which it plunges; in other cases, the river itself 
has made the falls. If a stream flows over the edge of a 
hard layer that rests on a softer material, the latter will be 
more quickly removed; moreover, as the softer layer is 
worn away, the height of the fall becomes greater and the 
water acquires an increased cutting power because of its 
greater fall; a cataract therefore results. 

In this manner the falls of Niagara River were formed. 
There, an upper layer of hard limestone surmounts sev- 
eral layers of softer rock. The upper layer offers consid- 
erable resistance to the water; the lower rock is easily cut 



126 



PHYSICAL GEOGRAPHY 



away. Hence the falls are increasing rather than decreas- 
ing in height; but the upper layer, however, is being under- 
mined and the falls are receding upstream at the rate of 
about two and one-half feet a year. 







^ -^T ^fiygg 



A SECTION OF A WATERFALL 



As Niagara River flows toward Lake Ontario, it encounters a layer 

of hard Niagara 
limestone that 
comes to the sur- 
face midway be- 
tween the two 
lakes. When the 
river reaches the 
edge of this hard 
stratum, it pitches 
a depth of IGOfeet. 
Below the Niagara. 
limestone are soft 
shales, sandstones, 
and a layer of hard 
limestone. The fall- 
ing water beats 
these away, clearing a deep pool under the cliff of Niagara limestone. 
The edge of the latter breaks off, the underlying strata wear back- 
ward, and the whole front of the falls recedes. 

At the point where the angle in the ledge is formed, the recession since 
1875 has been more than two hundred feet; at the American Fall, since 
1842, it has been very slight. It is a question of time only until the 
Canadian Fall will recede to a line between Dufferin and Sister Islands. 
When this has taken place the American Fall will have nearly or quite 
disappeared. Had the conditions of a hard stratum at the top and a 
softer one at the bottom been reversed, there would now be no cataract , 
even had there been one at the beginning of the present epoch. The 
softer rock would have been worn away until the perpendicular front 
had become an incline extending to a point below Whirlpool Rapids; 
and instead of the sublime cataract, there would now lie a succession of 
rapids like those which mark the passage of St. Lawrence Liver. 

Many cataracts are the result of accident. Thus, a flow 
of lava across Columbia River dammed the channel and 



THE WASTING OF THE LAND: RIVERS 127 



formed rapids at several localities. A similar lava flood 
obstructed its chief tributary, the Willamette River, form- 
ing the cataract at Oregon City. 

Falls and rapids are rarely found in the flood-plain age 
of a river, because in the formation of the flood-plain all 
inequalities are buried. After the stream has carved away 
its flood -plain, 
it may uncover 
and develop its 
former rapids 
and cascades. 

Migration of 
Divides. — As a 
general rule, a 
stream works 
most actively in 
the upper or 
montane part, 
where its cur- 
rent is swiftest. 
As the head- 
water streams 

deepen their gullies they frequently extend them backward ; 
a very vigorous stream may even cut its channel back- 
ward across a ridge. The crest of the latter then ceases 
to be the water-parting; the divide therefore is said to 
"migrate." 

In cutting its channel backward across a ridge or height 
of land a stream sometimes captures and diverts a feebler 
stream flowing on the opposite side of the divide. Most 
of the " wind gaps" of the Appalachian region are the results 
of this sort of river piracy. They are abandoned stream 



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THE RECESSION OF NIAGARA FALLS 



128 PHYSICAL GEOGRAPHY 

channels. They have been abandoned because the former 
occupants have been captured farther up the valley by a 
more vigorous stream which crossed the divide to get it. 
At least one stream in Northwestern Ohio and several 
in Pennsylvania have obtained some of their headwater 
tributaries by the robbery of neighboring streams on the 
opposite side of the divide. The Vistula has probably 
gained some of its headwater tributaries in this manner. 

Unusual Adjustments. — In selecting a new channel, 
or in adapting itself to the changing conditions of an old 
one, a river is said to adjust itself. Several causes may 



TUOLUMNE RIVER, CALIFORNIA 

The old stream channel is under the lava cap which jorms Table Mountain: the present chan- 
nels are at the base oj the mesa. 

compel a stream to change its course. It may clog its 
channel with sediment, or the latter may be obstructed 
by accident. Thus, by long-continued silting, the Hoang 
River, "China's sorrow," built its channel higher than 
the divide, near the top of which it flowed. In bS,52, din- 
ing a season of high floods, the river broke through its 
banks. Before that time it had flowed southeasterly into 
the delta of the Yangtze; after the break its course lay in 
a northeasterly direction into the Gulf of Pechili. 

The flood of lava that covered the area now called the 
plains of the Columbia, buried beneath it a long stretch of 



THE WASTING OF THE LAND : RIVERS 129 

the river basin, and the river was forced to make a new 
channel around the lava. Tuolumne River, California, was 
similarly buried, but finally succeeded in making another 
channel around the obstruction. 

In several other localities the Columbia has cut its channel through 
similar obstructions. In at least one case the river reclaimed its former 
channel by cutting through the entire thickness of lava, to a depth of 
about 2,500 feet. Deschutes River, a tributary of the Columbia, is 
readjusting itself by cutting a new channel into the same sheet of lava. 

It is highly probable that Saskatchewan River formed 
the upper part of the Missouri, and that the uplift of the 
height of land across its course cut the river in two. The 
waters of the Saskatchewan were ponded, forming Lake 
Winnipeg. The latter then overflowed its rim and found an 
outlet into Hudson Bay. 

The Work of Man.— By cultivating the land, man is 
indirectly responsible for the abnormal conduct of certain 
rivers. In order to make his land productive the farmer 
must not only clear it of growing timber and destroy the 
smaller vegetation, but he must also provide rapid drainage. 
Forest growths, shrubbery, and sod all serve to retain water 
in the soil and therefore prevent rapid drainage. 

The removal of vegetation has exactly the opposite 
effect. The rainfall is rapidly collected by the tributaries, 
and as quickly poured into the main stream. As a result, 
high and quickly-forming floods occur. In late years the 
Ohio and the Susquehanna have suffered much from dis- 
astrous floods, and these are largely a result of deforesting 
their watersheds. 

Geographical Distribution of Rivers. — Rivers are 
the offspring of rainfall and, as a rule, regions of great 
rainfall are regions of the largest and most numerous rivers. 



130 PHYSICAL GEOGRAPHY 

This is shown in the case of the Amazon and the Kongo. 
Both rivers are situated within the belt of equatorial rains. 
Each has a large number of great tributaries, and cadi 
discharges an enormous quantity of water. 

A river cannot develop great length and size unless its 
watershed is also large. When Columbus entered the mouth 
of the Orinoco, heat once declared the country southward 
to be a continent, because so large a river could not exist 
on a small body of land. 

There is no apparent law governing the distribution of 
rivers except the position of slopes and the amount of 
rainfall. The largest rivers are not in the largest conti- 
nents, nor are the longest streams in regions of greatest- 
rainfall. The Atlantic receives the waters of more large 
streams than any other ocean; the Arctic Ocean is the 
next in order. The reason therefor is the fact that the 
largest plains slope toward these two oceans. 

The plains and slopes of the Western Continent receive 
the full benefit of moisture-laden winds; and the rivers, 
as a rule, reach a higher state of development than those of 
the Old World. The Mississippi and the Amazon drain 
watersheds each half as large as Europe. The Mackenzie, 
La Plata, Yukon, Columbia, and Colorado about equal in 
size the great master streams of the Old Work 1 . 

The broadest part of South America is crossed by the 
tropical rain belt, and therefore is in the region of heaviest 
rains. The ocean winds have a sweep of about 2,500 miles 
before they are arrested by the Andes Mountains; and 
because precipitation covers such an enormous area, there 
necessarily results a river system of vast proportions. The 
Amazon discharges a greater volume of water than any 
other river. 



THE WASTING OF THE LAND: RIVERS 131 

Most of the chief plain of the Old World faces the Arctic 
Ocean. It is the largest plain in the world, and is drained 
by large rivers. None of them equals the Amazon nor the 
Mississippi-Missouri, however, for the reason that they 
are situated in a region of moderate rainfall. The Yangtze 
and the Amur are the most important rivers of the Old 
World, and each has a large commerce. The^three large 
rivers of the Indian Ocean are commercially of very great 
importance. 

The southern part of Europe does not extend into the 
region of tropical rains; hence the absence of large streams 
on the southern slope. The southern part of Asia is un- 
der the tropical rain belt, but the drainage slope is com- 
paratively short, and but few large streams have formed. 
Thus it may be seen that the large plain of Eurasia is un- 
favorably situated for large rivers. On the other hand, 
the areas which are favorably situated are too small for 
the development of great streams. The great number of 
smaller rivers compensates for the absence of such rivers 
as the Amazon. 

Africa possesses several large rivers, two of which, the 
Kongo and the Nile, are of great importance. Like the 
Amazon, the Kongo is an equatorial stream, and the two 
are much alike. The Nile is remarkable for its annual 
overflows, and from the fact that in the lower 1,200 miles 
of its course it receives not a single tributary, a result of 
the rainless region through which it flows. 

Australia possesses but few permanent streams, and 
these are of small gig© This continent is unfortunately 
situated. It is under the Calms of Capricorn, and it con- 
tains no high mountain-range. The Murray-Darling is the 
only river of importance. In the summer season most of 



132 PHYSICAL GEOGRAPHY 

the streams disappear altogether, or else form a succession 
of shallow pools. 

Continental Rivers. — There are several large areas 
that have no drainage to the sea. Such rivers are there- 
fore called continental rivers, and their watersheds, inland 
basins. Where is the continental region of Eurasia ? Name 
the four largest rivers. In Africa the only large continent al 
rivers are those flowing into Lake Chad. There are many 
continental rivers in Australia. Practically all of them 
are dry in summer and some are filled only when an oc- 
casional cloud-burst pours a flood of water into their 
channels. 

The Humboldt, Carson, and Jordan are the principal 
continental streams of North America. What do they 
indicate with reference to rainfall? In South America the 
Desaguadero, the outlet of Lake Titicaca, is the principal 
continental stream, although one or two of the larger rivers 
in Argentina are occasionally cut off from the sea. 

As a rule, continental rivers, are a result of scanty rain- 
fall. An increase of rainfall would swell the volume of the 
river until its waters finally reached the sea. The soil of 
an enclosed basin is usually rich, because none of the nu- 
tritive elements are leached out of it by storm waters. 

Economic Importance of Rivers. — Rivers are the 
most important highways of commerce and are the lines 
along which civilization and settlement penetrate to the 
interior of a country. Merchandise; can be carried by means 
of river navigation at a less cost than in airy ether way. 
iviosi 01 Cim grtsA migE&&©&£ " f . peoples , have followed the 
valleys of rivers; and in mountainous regbnTSeluTtivateci 
areas are confined mainly to their narrow flood-plains 
Outside the Great Central Plain of the United States most 



THE WASTING OF THE LAND: RIVERS 133 

of the railways of the country have been built along river 
valleys, so that these are "practically " lines of least resist- 
ance" to the activities of a people. 

In its relation to life and its industries, the flood-plain is 
the most important part of river physiography. The sur- 
face is always level, making the region accessible to trans- 
portation. Moreover, the rock waste is mixed with the ele- 
ments that form the food of plant life, and therefore the 
flood-plain has a most fertile soil. In the Mississippi 
Valley, for instance, where the bluff lands produce twenty 
bushels of wheat, the bottom lands yield thirty; and if an 
acre of bluff soil yields one bale of cotton, the same area 
of bottom lands yields two. The greater part of Chile 
is a . simoom-swept desert with scarcely a sign of life ex- 
cepting that which pertains to the mines and the mountain 
valleys. The real Chile is found in the densely-peopled 
flood-plains of the Andine streams. In these short valleys 
are concentrated nearly all the activities that go to make 
a great state. 

The Egypt of history is not found in the broad stretch 
of land lying between the Red Sea and the Libyan Desert. 
On the contrary, the four thousand 3 r ears of histor}^ that 
has so much to do with modern civilization dates back to 
the flood-plain of the Nile. 

QUESTIONS AND EXERCISES. — Under what conditions and 
at what times is the stream with which you are best acquainted 
muddy? 

Note and describe any place at which the stream is cutting away its 
banks. 

Note and describe some place where sediment is being deposited. 
If possible, account for the action in each case. 

An embankment of freshly turned earth receives the full force of a 
rainfall ; how will its general form most likely be affected? 




ISn Longitude ~T2<F West from 90' Greenwich 00 



136 PHYSICAL GEOGRAPHY 

What effect has sod, shrubbery, and forestry on a surface that is 
exposed to rain? 

Name some results that might occur if the channel of a stream were 
blocked. 

How would the Mississippi be affected if the Ozark highlands were 
elevated considerably higher? {See any good topographic model or 
relief map.) 

What effect will the approaching old age of the Mississippi have on 
the size of the Gulf of Mexico? 

On p. 123 is a map of Chesapeake Bay; make a sketch-map and 
restore the river channels on the supposition that the surface were 
uplifted until about the lowest point is higher than sea-level. 

Does the appearance of the canon of the Colorado River suggest an 
abundant or a scanty rainfall? How would a great increase in the 
rainfall affect the scenery so far as the topography of the valley is con- 
cerned? 

What does the absence of tributaries indicate concerning the rainfall 
of the lower Nile? 

From the cyclopaedia, or any convenient reference-book obtain a 
description of the Volga and its delta. 

Make a list of ten or more important cities situated on estuary 
mouths; — two on or near delta mouths. 

COLLATERAL READING 

Shaler. — Aspects of the Earth, pp. 143-196. 
Mill. — Realm of Nature, pp. 241-251. 

Davis. — Rivers of New Jersey. National Geographical Magazine. 
Mississippi River Commission. — Map of the Alluvial Valley of the 
Mississippi River. 

Powell. — Physiography of the United States, Monograph II. 

Russell. — Rivers of North America. 

Hall. — Geography of Minnesota, pp. 109-149. 



CHAPTER VIII 

THE WASTING OF THE LAND: THE WORK OF UNDER- 
GROUND WATERS 

About as much water sinks into the porous rock waste 
as gathers in the various external channels. Telluric, or 
underground waters, may not be so active in wearing away 
the rock envelope as are the surface streams, but they are 
very important factors in shaping the earth's topography. 
Surface streams flow quickly away in their channels, but 
the underground waters must slowly force their way through 
channels that are ill-adapted to the work; they must also 
keep these passages clear of obstructions. The work of 
underground streams is vastly more difficult than that of 
surface waters. 

If the prevailing rock of a region be clay, or slate, or 
other impervious rock, the underground drainage will be 
close to the surface, for such rocks not only prevent the 
passage of water, but most of them are insoluble. In such 
cases the water must trickle through the top soil much in 
the same way that water passes through a filter made of 
sand and gravel — that is, it must flow in the spaces be- 
tween the particles of rock waste. 

If the rocks are near the surface and the amount of water 
is considerable, swamps may result. That is, swamps may 
be an incident of imperfect underground drainage, as they 
are of imperfect surface drainage. 

On the other hand, if the rock of a region is mainly of 

137 



138 PHYSICAL GEOGRAPHY 

limestone, and more especially if the strata be broken and 
faulted, underground drainage is usually extensive. The 
fissures between the faulted strata are likely to become 
the channels of springs. Not only does the water clear a 
passage for itself along the lines where the rock is broken, 
but it also dissolves enough of the limestone to make 
caverns of vast extent. Singularly, however, the channel 
may be filled up subsequently with the mineral matter 
deposited from the water itself. 

It must not be assumed, however, that these waters al- 
ways remain underground. On the contrary, they are con- 
stantly in motion, and they finally emerge to the surface. 



.'-o_V "■■■'"- '"-—"";-"-"' ' __/ "~-' r -'-Zi— ■ ^ r ^ l 'i lj ^bjt \ Water Level 

\^f-iL-^^ ^"'^^Cl-^V s l>rlngs 

DIAGRAM SHOWING THE FLOW OF PERCOLATING WATERS 

Underground waters are of three kinds — percolating waters, 
springs and artesian wells, and underground streams. 

Percolating Waters. — When water sinks into porous 
ground it fills the spaces between the grains of sand, gravel, 
or other soil. Some soils are so porous that a cubic foot 
will contain more than one-quarter of its bulk of water. 
The latter sinks through the ground until it meets a layer 
of rock through which it cannot pass. It therefore ac- 
cumulates until its level is as high as the rim of the im- 
pervious rock. 

Flowing over the lowest part of this rim, it goes on, per- 
haps to fill a similar basin lower down the slope; possibly 



UNDERGROUND WATERS 139 

it comes to the surface in the form of a swamp, a pond, 
or a lake. If the plain or slope is traversed by a river val- 
ley a great deal of the water oozes through the soil into the 
stream. In many instances waters of percolation are an 
important supply of streams. 

This may be seen in the cases of streams that flow through a region 
of pervious soil. Such streams steadily increase in volume, although 
for many miles they receive no apparent tributaries. As an example, 
Spanish Fork, on the west slope of the Wasatch Mountains, receives 
only two or three small tributaries from the summit to the base of the 
mountains. It begins as a rivulet, scarcely larger than one's arm; 
it reaches the base of the range, a mountain torrent twenty feet across. 
Most of the increment is due to percolating water. 

Wells are always filled by percolating waters, and to ob- 
tain an abundant supply it is necessary only to sink a shaft 
below the level of the water. Unless the well is so shallow 
as to catch the surface drainage, the water is usually cold 
and wholesome. 

If the area of porous soil is large and has a considerable 
depth, an enormous quantity of water may be held. The 
city of London is supplied with water that percolates through 
the adjacent chalk-beds. The water supplies of many of 
the towns and villages of the high plains east of the Rocky 
Mountains are derived in a similar manner. 

The "sand valleys" of Western Kansas, Nebraska, and 
Dakota furnish an excellent example of percolating waters. 
The storm waters falling in these valleys are almost all ab- 
sorbed and held in suspension by the deep deposits of 
porous rock waste. During dry seasons these sand valleys 
furnish about the only supply of water to the people liv- 
ing in that region. The amount thus held in the porous 
rock waste is generally sufficient to irrigate the crops that 
otherwise would perish from drought. 



140 PHYSICAL GEOGRAPHY 

These accumulations of sand, though apparently hills, in most cases 
are valleys filled with rock waste carried thither by winds. In the 
holding of water capillary attraction is not only an agent of accuni illa- 
tion, but one of retention, also. 

The Fresh Water of Islands. — The water supply of 
small and low islands is obtained in a similar manner. 
The storm waters fall on the island and immediately sink 
into the sand until they reach salt water. But inasmuch 
as the fresh water is lighter it rests upon the surface of the 
salt water without mixing with the latter. 

Artesian Wells. — Underground waters are often con- 
fined between strata of impervious rock. In such a case, 
if the porous layer is reached by boring, the water will be 




THE WATER SUPPLY OF LOW SANDY ISLANDS 

The lighter jresh water rests on the sea water. 

forced up the bore to its normal level. Artificial springs 
of this character are called artesian wells. The "driven" 
or "piped" wells so common throughout the Mississippi 
Valley and the prairie region are also examples of such wells. 
These wells are shallow, however, and tap only the super- 
ficial percolating waters. The water is usually brought to 
the surface by ordinary lifting pumps. 

In some artesian wells, however, the water is forced to 
the surface, not by gravity, but by the pressure of the air 
or other gases within the reservoirs. In the "gas belt" of 
the Middle West there are many instances of this sort. 

Along the low coast plain of Southern California many 
artesian wells have been driven, and many acres have been 
made productive thereby. The first wells were spouters, 



UNDERGROUND WATERS 



141 



but subsequently the water failed to reach the surface un- 
less forced. Many artesian wells have been bored in the 
Sahara. 

The amount of desert land made productive solely by artesian wells 
is not very great. As a matter of fact, not all the artesian wells in the 
world would supply an area equal to that of Delaware with the water 
necessary to produce its crops. 

Springs. — A small stream of water issuing naturally 
from the ground is a spring. In some cases the water spurts 
from a sloping wall, such as the face of a cliff, but in most 
instances it gushes out of comparatively level ground near 
the foot of a slope. Usually the discharge does not amount 




THE WATER SUPPLY OF ARTESIAN WELLS 
The porous stratum of the anticline is both covered and underlaid with impervious rock. 

to more than a few gallons per minute, but sometimes 
it is sufficient to fill the channel of a good-sized stream. 

The difference between springs and percolating waters is mainly 
one of degree; issuing from a channel it is a spring, but if the water 
merely oozes through the soil it is an example of percolation. In 
Florida several springs, so-called, discharge an amount of water sufficient 
to fill a river bed. Orange and Silver Springs are so large that small 
river craft easily enter the mouths. As a matter of fact these springs 
are the exits of underground rivers. 

As a rule, a spring makes its channel. Sometimes the 
force of the flowing water is sufficient not only to force a 
passage, but also to keep it clear; in many cases the water 
makes a channel by dissolving a part of the rock through 
which it flows. If the quantity of material dissolved be 



142 PHYSICAL GEOGRAPHY 

considerable, a mineral spring results. Such springs are 
very common. Those at Saratoga, Vichy, and Carlsbad, 
are known all over the civilized world. 

In volcanic regions, where the rocks are seamed with 
fissures, the water trickles downward until it conies in 
contact with heated rocks, and when it again emerges to 
the surface the water may be at a boiling temperature; it is 
therefore a hot spring. 

So long as the mouth of a spring is lower than the sur- 
face of the waters from which it is derived, the spring will 
continue to flow, and will be a constant spring. If it be 
situated in a region of periodical rains it is apt to be a 
periodical spring — flowing during the rainy season only. 
If the flow depends partly on the pressure of air or other 
gases, an intermittent spring may be formed. 

From time immemorial the periodical spring has been explained by 
the existence of a siphon-shaped channel. Doubtless such channels 
occur, but not a single one is known to exist. In a few instances the 
pressure of accumulating gases is known to be a cause of intermittent 
flow, but in the great majority of cases the cause of periodicity is un- 
known. One of the most remarkable periodical springs occurs in Pales- 
tine near the old convent of Mar Jirius. This spring is quiescent for 
about two and a half days; then its flow begins, lasting for several hours. 
It is probable that the stream flowing from this spring is the Sabbatic 
River described by Josephus, which rested for six days, flowing on the 
seventh. 

A spring near Rogersville, Tennessee, is celebrated for the enormous 
quantity of water ejected. Its period of flow occurs about every half 
hour, lasting only a few minutes. The Bullerborn, once a famous 
intermittent spring of Westphalia, has now a constant flow. In regions 
of very high tides, periodical springs are sometimes formed by tidal 
action. The fresh water is pushed back by the tide, until it emerges to 
the surface through self-made channels. 

Geysers. — In certain volcanic regions there are springs, 

which at intervals eject great quantities of hot water 



UNDERGROUND WATERS 



143 



and steam at regular intervals. The eruptions occur with 
almost clock-like regularity. These are called geysers. 

The essential feature of the geyser is a long, irregular tube 
that extends deep into hot 
volcanic rocks. The tube 
is formed probably by the 
water itself which, when 
cool, deposits the silica 
which its waters had pre- 
viously dissolved. 

The water that collects 
in the lower part of the 
tube becomes heated far 
beyond the temperature 
at which water ordinarily 
boils, but boiling is pre- 
vented by the great weight 
of the water above. Fi- 
nally a little steam is 
formed, and some of the 
water is forced out at 
the top of the spring. As 
soon as this occurs, the 
pressure being relieved, 
the superheated water 
flashes into steam — not 
gradually but explosively. 

Eruptive springs of this 
character are not common; 
but three regions are 

known in which they occur — Iceland, Yellowstone Na- 
tional Park, and Northern New Zealand. Hot min- 




A GEYSER, YELLOWSTONE NATIONAL 
PARK 



144 PHYSICAL GEOGRAPHY 

eral springs occur in many other localities, but they arc 
not eruptive. 

The geyser region of Iceland has been known for more 
than a century. It is near active volcanoes and includes 
about one hundred eruptive springs. The New Zealand 
group, situated near the volcano Tarawera, is small in area, 
and contains but few spouting springs. 

Yellowstone National Park, Wyoming, contains several 
groups of geysers, mainly in the basin of Firehole River. It 
comprises more than ten thousand ge3^sers and hot springs. 
Of this number about twoscore discharge water to a height 
of one hundred feet or more; one, the Giantess, spouts a 
column of water two hundred and fifty feet high, while the 
steam is forced nearly a thousand feet higher. Geyser 
eruptions occur at periods varying from thirty minutes to 
about as many hours. Each is preceded by a gentle over- 
flow of water, and commonly lasts from a few seconds to 
fifteen minutes; but the eruptions of several continue for 
about two hours. The intervals between eruptions rarely 
vary more than a few minutes, but careful observations 
show that their length is increasing, and the energy of 
eruption is diminishing. The flow of many has ceased 
altogether. 

The deposition of silica from the cooling waters forms 
terraced basins. As a rule, the deposits thus produced 
are richly colored with variegated bands. Tin 1 " Pink-and- 
White Terraces" of New Zealand derive their name from 
this fact. 

Mud Volcanoes. — Mud volcanoes are hot springs thai 
have piled cone-shaped mounds of mud about their vents. 
The mud ultimately hardens into a compact mass. Steam 
and sulphurous gases are commonly the products of these 



UNDERGROUND WATERS 145 

alleged volcanoes. The energy displayed is feeble, and the 
mud cones are seldom more than twenty or thirty feet high. 
The mud consists of fine clay formed from the mifferal matter 
of the spring. Mud volcanoes are common in all volcanic 
regions, and it is thought that the gases given off by decom- 
posing rock create the energy necessary for the miniature 
eruptions. But this is not true of all. 

Underground Streams. — In addition to the multitude 
of surface streams, much water finds its way to the sea — 
not simply by percolation but in underground streams. 
The run-off of streams is mainly above ground, but a con- 
siderable part of a stream may, and usually does flow below 
the surface. 

There are several reasons for this. In the first place, 
whenever a stream flows in a gravelly channel, a great deal 
of the water sinks into the gravel and flows along the bed- 
rock bottom. The same is true of rivers that flow through 
light, sandy rock waste, such as those of the Basin Region 
of the Rocky Mountains. The underground flow of such 
rivers is strong even during the fierce heat of summer. 

In the daytime, the enormous evaporation frequently causes the wa- 
ter to disappear. In the night, or during cloudy days, when evapora- 
tion is lessened, the percolating waters rise to the surface. This phenom- 
enon is occasionally noticed in the lower courses of Humboldt, Carson, 
and Reese Rivers, in Nevada. The underground part of the river is 
nearly always to be found. 

In many instances small stream channels have been ob- 
literated by filling or grading. Now, although the surface 
flow may be destroyed, the underground current is not; on 
the contrary, it is apt to be strengthened. Thus, in some 
of the larger cities many drainage courses have been covered 
up in making streets, and it has been found necessary 



146 PHYSICAL GEOGRAPHY 

to excavate many of these old water-courses and sewer 
them. 

In most large cities of America and Europe the channels 
of such streams are plotted, and drainage maps showing 
their former courses are in common use by engineers and 
builders. Not infrequently these streams, becoming ob- 
structed, have forced their way to the surface and flooded 
the streets. Such experiences occur in almost every large 
city. 

Considerable trouble from this cause occurred near the junction of 
Oxford Street and Edgeware Road, London, the reason being that the 
famous Tyburn flowed in this locality. About four hundred square 
feet of Broadway, New York, recently caved in from a similar cause. 
The foundations of a costly church in Philadelphia sank in the quicksand 
and the large sewer under one of the principal streets has caved in several 
times — all because they were undermined by buried streams. 

" Lost" Rivers. — Of still greater interest, though not 
more important, are "lost" rivers. These streams receive 
their name because they flow for a part of their courses on 
the surface, and then disappear to flow through sub- 
terranean channels. The waters of some lost rivers dis- 
appear by percolation, but in most instances the stream 
pitches into its underground channel through a "sinkhole." 

Underground rivers are very common in the limestone 
area of southern Indiana, Kentucky, and Tennessee. One 
of these rivers winds its way beneath the floor of Mammoth 
Cave. Its waters contain fish and two or three species of 
insect life that have rudimentary eyes only; they have no 
use for perfect organs, for no light penetrates to their aboi le. 

At Orangeville, Indiana, an underground stream comes to (lie surface 
and flows with sufficient force to turn a mill-wheel. Only a lew miles 
away, Lost River, a considerable stream, sinks out of sight. San Pedro 
Springs, near San Antonio, Texas, is the outlet of an underground 



UNDERGROUND WATERS 147 

stream. Giant Spring, near Great Falls, Montana, is the outlet of Little 
Belt River, which disappears and flows underground for thirty miles 
of its course. In Alabama, the engineers of a railway discovered an 
underground stream sixty feet below the bed of Coosa Ri^-er. 

According to Greek legends, the Alpheus, the river of Peloponnesus, 
which Hercules turned through the Augean stables, sank underground 
and emerged to the surface somewhere in Sicily. As a matter of fact 
a considerable part of the course of the Alpheus is underground; and 
there is also a spring in Sicily discharging a large volume of water. It 
is hardly necessary to add that the two have no connection. 

Similar streams are found in Weir's Cave, in Luray Cavern, and, in 
fact, in almost every limestone cavern. In Derbyshire, England, the 
Hampo and the Manifold flow many miles through underground pas- 
sages. In both instances the identity of the stream is proved by 
throwing a floating body into the water above the beginning of its under- 
ground course and capturing it when it reappears. 

In Southern California, where water is required for ir- 
rigation, underground streams have been forced to the sur- 
face by building dams across them where they emerge from 
the canon. The clams extend from the surface of the ground 
down to bed-rock. The water is thereby forced to the 
surface. Where such submerged dams have been con- 
structed, the artesian wells in the plain below are seriously 
impaired, the flow of water being greatly reduced. 

Physiography of Underground Waters. — The work of 
underground waters is by no means so extensive as that 
of surface waters, but it is, nevertheless, of great im- 
portance. Water has a great solvent power; hot water, 
especially if under pressure, will dissolve rock that is not 
affected by cold water. When the solution cools, much of 
this matter is again set free. In the meantime, if the water 
has been forced to the surface, the substances dissolved 
will be carried along and there deposited. 

Sometimes the deposits are spread over the surface of 
the ground, forming sinter or tufa. If the latter happens 



148 



PHYSICAL GEOGRAPHY 



to cover loose rock waste or soil, a cavern or cave will re- 
sult if the material under it be removed. 

In other instances the hot mineral waters flow into deep 
fissures in the rocks. As the water cools the mineral mat- 
ter is deposited on the walls of the fissure until, finally, 
the latter is filled, thereby forming a mineral vein or lode. 
All through mountain regions, veins of banded or " ribbon" 
rock containing the ores of gold, silver, copper, lead, and 




BLUE GROTTO, ISLANT) OF CAPRI, ITALY 



other valuable metals have been deposited in such fissures. 
Thus underground waters are a. vehicle by which many 
useful metals are carried from the interior to the surface 
of the earth. 

Caverns. — Most caverns and caves are formed by under- 
ground waters. The water dissolves the rock and carries 
it off, leaving a cavern. Clay, slate, granite, and sand- 



UNDERGROUND WATERS 



149 



stones are not readily dissolved; 
and in regions underlaid by such 
rocks, caverns are rare. Lime- 
stones, on the contrary, are solu- 
ble, and in localities where they 
prevail, caves and caverns are 
common. A joint or fault in the 
rock is usually the beginning of 
the formation of a cavern such as 
is shown in the accompanying 
illustration. Along this line the 
water can readily collect. There- 
after the formation of the cavern 
is a question of time and the 
solubility of the limestone. 

In the cavern district of Ken- 
tucky, Tennessee, and Virginia 
small pieces of sharp flint are 
plentifully distributed through- 
out the limestone. These are 
tossed about and carried along 
with the water and thus become 
powerful cutting tools. 

Mammoth Cave, Kentucky, is a laby- 
rinth of passages aggregating more than 
two hundred miles; the length of the 
cave on a straight line is about ten 
miles. Some of the vaults and domes 
are two hundred and fifty feet high. 
There are other caves in the vicinity 
nearly as large. Weir's Cave and Luray 
Cavern, both in Virginia, are smaller 
than Mammoth Cave. Howe's Cave, 
Schoharie County, New York, is one 



150 



PHYSICAL GEOGRAPHY 



of the few large caverns of interest in the northern Appalachian region. 
In the grotto of Lueg, Illyria, there are three galleries, one over another. 
The cavern of Adelsberg, Austria, is the abandoned channel of the Poik 
River. Its length is about two miles; its labyrinthine passages aggre- 
gate many miles. A considerable part of the course of the Poik is 
underground. Probably the underground passage and caverns of the 
Tirnavo have been more thoroughly investigated than those of any other 




A SINKHOLE, EDMONSON COUNTY, KENTUCKY 
The Ihroal leading to the cavern below has hen artificially closed. 

stream. The river flows to the Adriatic, a few miles north of Trieste, 
and its character has been known for more than two thousand yens. 
Concerning it Virgil wrote: 

. . . et fontem superare Timnvi 
unde per ora novem vasto cum murmure montis 
it mare proruptum, ct pelago preniit arva sonant i. 

— .Eniid I., 247. 
Virgil's description is no longer true of the delta, for the nim mouths 
have become only three in number. 



UNDERGROUND WATERS 151 

Between the solvent power of the water and the 
incessant cutting done by the flint particles, the under- 
ground channel is worn deeper and wider till a cavern, 
perhaps a score of miles long and many feet deep ; is 
formed. 

But the forces that made the cavern just as surely will 
destroy it. Surface waters are constantly wearing away 
the rock that forms the roof of the cavern. In time, holes 
are worn through the roof and sinkholes are formed. These 
increase. in size and in number until the roof is destroyed. 
The stream then becomes a surface river flowing in a lime- 
stone canon. Natural Bridge, in Virginia, is a remnant of 
one of these roofs; the rest of the roof has been carried 
away. 

Many natural bridges of similar origin exist. Near Bogota, Colombia, 
a natural arch spans a chasm nearly four hundred feet deep. A natural 
bridge spans Pine Creek, in Gila County, Arizona. The arch is about 
four hundred feet wide and the span is about a thousand feet in length. 
The underside of the arch is water-worn, but since it was formed the 
creek has cut its channel more than two hundred feet downwafd. In 
some instances the arch more properly constitutes a tunnel. One, near 
Clinch River, Virginia, is more than half a mile long, and is a part 
of the route of a railway. Nearly always a stream of water flows under 
the arch of a natural bridge, and its current carries away the fragments 
that fall from the roof. 

In the course of time caverns are apt to be filled up by 
limestone itself. The water charged with limestone leaks 
or filters through the top of the roof drop by drop. The 
water leaves a minute portion of limestone at the roof; at 
the floor of the cavern a little more is deposited. So, 
little by little, the limestone gathers into icicle-shaped 
columns, both at the roof and the floor of the cavern. The 
former are called stalactites, the latter stalagmites. Finally 



152 



PHYSICAL GEOGRAPHY 



the two join, forming a single column, and as the water 

trickles down their sides they increase in size, and thus fill 
the cavern. 

Subsequently, perhaps, this same mass of limestone may 
be dissolved away and redeposited elsewhere. Ai all 
events, the process illustrates the general law that governs 




A PASSAGE IN LURAY CAVERN— STALACTITES AXD STALAGMITES 

cavern-formation in these regions. Water in motion dis- 
solves limestone and makes caverns; still water deposits 
limestone and fills them up. 

QUESTIONS AND EXERCISES.— If possible find the depth of 
each of half a dozen or more wells in the neighborhood in which you 
live : compare the distance of the surface of the ground to the surface 
of the water in the wells. 



UNDERGROUND WATERS 153 

To what depth must a well be sunk before it will fill with water? 

Will one be apt to find percolating waters in regions having but 
very little rain? 

Explain why water in very shallow wells is apt to be impure. 

How do springs become "mineral " in character? 

Why does rain water contain no mineral matter in solution? 

Why are geysers and hot springs confined usually to volcanic 
regions? 

Under what circumstances or conditions can water be heated above 
the ordinary boiling point? (See almost any text-book in physics.) 

Describe a way in which caverns may be formed at the foot of sea 
cliffs that face heavy waves. 

How are the sinkholes in the limestone regions formed? 

By using lime-water such as is obtainable at the druggist's, suggest 
a way in which stalactites may be artificially formed. 

COLLATERAL READING 

Shaler. — First Book in Geology, pp. 66-87. 

Shaler. — Aspects of the Earth, pp. 96-142. 

Powell. — Irrigation and Artesian Wells, pp. 203-290. United 
States Geological Survey, 11th Annual Report, Part 2. 

Le Conte. — Elements of Geology, pp. 103-113. 

United States Geological Survey. — Map of Yellowstone National 
Park. 



CHAPTER IX 

THE WASTING OF THE LAND: THE WORK OF 
AVALANCHES AND GLACIERS 

Snow and ice are also important agents in the waste of 
the land. A great deal of the moisture of the air falls in 
the form of snow. Very cold regions excepted, the snow 
that falls below three or four thousand feet melts with the 
coining of spring and flows away in the various stream 
channels. In high mountain regions some snow falls on 
slopes whose temperature is rarely higher than the melting 
point of the snow. In such localities, therefore, but little 
of the snow can melt. 

Snow rarely accumulates to a depth of more than ten or twelve feet 
on a level area. On mountain slopes, however, the snow is not evenly 
distributed, most of it finally lodging in ravines and places not exposed 
to the sweep of the wind. In laying the foundations for the observa- 
tory at the summit of Mont Blanc, the snow and ice were so deep that no 
rock bottom could be found at a depth of sixty feet. On the western 
slope of the Sierra Nevada Mountains the accumulation of snow .sonic- 
times reaches twenty feet on the level, while the drift may be much 
thicker. 

In the Alps and the western United States, the heaviest 
snows fall between the altitudes. of six thousand and nine 
thousand feet. Very little accumulates below four thou- 
sand feet, and but little falls above twelve thousand feet. 

At high elevations, even though the fall may be slight, 
one might suppose that the accumulation would increase 
indefinitely; but in high mountain regions various agencies 

154 



WORK OF AVALANCHES AND GLACIERS 155 

prevent such accumulation. Among them are evapora- 
tion, wind, avalanches, and glaciers. They not only remove 
the snow and ice, but they are also powerful factors in 
wearing away the land and in transporting rock waste. 

Evaporation is active in the removal of snow. Ice and 
snow evaporate just as does water; and at great heights, 
where the air does not press so heavily as at sea-level, 
evaporation is sometimes rapid. 

This is seen when frozen roads become dry and dusty without thaw- 
ing. Wet clothing hung out to dry in very cold weather first freezes 
and then gradually dries. An inspection of Table III., Appendix, shows 
that even at a temperature of — 40° F. a small amount of moisture may 
still exist in the atmosphere. 

Winds are also a potent factor in the removal of snow. 
In high mountain regions the wind has a terrific force, and 
the gales that rage among snow-covered peaks quickly drift 
the dry snow-dust into ravines and canons. The power of 
wind in drifting loose soil has already been noted. But 
snow is less than one-quarter as heavy as soil; hence the 
work of wind is far more effective. 

There are two factors at work, that are interesting, not 
only because they remove ' an enormous amount of snow, 
but in transporting it they become physiographic agents of 
great importance. These are avalanches and glaciers. 

Avalanches. — When a great body of snow, resting on a 
steep slope, suddenly slips and plunges down the incline, 
the moving mass is an avalanche, or challanche. Excepting 
the kind of material transported, which is mainly snow, 
the avalanche does not differ from an ordinary landslide. 
But although a second landslide rarely takes place in the 
same track, an avalanche may occur every time the snow 
falls on the slope. The snow accumulates on the steep 



156 



PHYSICAL GEOGRAPHY 



slope until its great weight causes il to slip, and the great 
mass gathering speed, moves downward with a terrific roar. 

In certain parts of the Rocky, Cascade, and Sierra Nevada Mountains 
avalanches are frequent, but they are not so common as in the Alps. 

In the Alps, where the slopes are steep, avalanches occur 
frequently and regularly. In many places the avalanche 

tracks are as definitely 
marked as river chan- 
nels. Indeed, one may 
consider an avalanche 
track as the torrential 
part of a stream whose 
flow is occasional and 
spasmodic. Like the 
mountain torrent, too, 
it carries to lower lev- 
els an enormous amount 
of rock waste. Not only 
are avalanche courses 
distinctly marked, but 
expert mountaineers are 
able to predict the oc- 
currence of snowslides 
with great certainty. The avalanche, therefore, is a feature 
of mountain economy not less normal than the mountain 
torrent. 

The most destructive avalanches occur in the first hours 
of sunshine, just after a snow-storm. The flakes are then 
so fine and smooth that almost any disturbance will start 
them. A footstep or a gust of wind imparls motion to a 
handful of snow, and it begins its descent. Gathering fresh 




AVALANCHE BASIN, MONTANA 

Thr slopes are Inn sleep to permit the accumulation 
oj snow, and the latter, gathering within the 
basin, lias formed the lake at the button! oi the 
clij]. 



WORK OF AVALANCHES AND GLACIERS 157 

material as it advances, and increasing in velocity, it soon 
sweeps everything before it, carrying havoc and destruction 
perhaps into the region of cultivated fields, far beyond the 
foot of the slope. Rocks crash right and left and the whirl 
of the wind carries eddies of snow a thousand feet or more 
into the air. i 

These, the poudreuses (powdery snow), are the most dreaded of all 
snowslides. Damp snow does not shear and move readily; it is the 
light, dry snow, that has little or no coherence, that is the distinctive 
feature of this form of avalanche. 

When avalanches follow their customary tracks they are 
neither especially dangerous nor destructive, unless they 
reach beyond their ordinary limits. But sometimes they 
take place in localities previously free from them, and these 
are the cases in which the havoc is greatest. Not only is 
everything destroyed along the path of the moving snow, 
but the effects are even more apparent along the edges; for 
the blasts of wind set in motion by the avalanche, fell every 
vestige of timber, perhaps a thousand feet or more on both 
sides. Places that the experienced mountaineers have dis- 
covered to be possible avalanche tracks, are now artificially 
guarded, in order to prevent, so far as possible, the forma- 
tion of dangerous snowslides. 

Another form of avalanche occurs in the Alps at the 
beginning of warm weather. Instead of light, powdery 
snow, its volume consists of ice and coarse snow mixed with 
rock waste. The lower part of the snow and ice are under- 
mined by water as the ground thaws. Finally the whole 
mass slides down the incline. These avalanches, which do 
not differ materially from landslides, are rarely destructive. 

Landslides. — The sudden descent of great masses of 
loose rock waste does not differ materially from the ava- 



WORK OF AVALANCHES AND GLACIERS 159 

lanche. It is the sudden degradation of a highland, and 
the transportation of rock waste to a lower level* 

The small landslides along railway cuts differ but little 
from those that occur on a larger scale on mountain slopes. 
A considerable volume of loose rock, undermined by water, 
slides to a lower level because coherence is weaker than 
gravity. Perhaps the loose material may rest on a sloping 
surface of rock. Possibly, running water may undermine 
a cliff until the overhang breaks and falls. In a few in- 
stances the landslide has been many acres in extent. 

Glaciers. — A great part of the snow that falls on high 
and steep slopes is either blown into ravines by the wind 
or is tumbled into them by avalanches. In the upper 
part of the ravine the snow is light and flaky, but farther 
down it has begun to melt, and instead of crystals it con- 
sists of little granules of ice, called neve. Still farther 
down the ravine, the neve has a striped or banded appear- 
ance. 

The bands are alternate layers of ice and dirty snow. The ice is 
formed of snow that has been subjected to great pressure. Because 
of the pressure all the air has been squeezed out, and for this reason the 
ice is clear and blue. The bands of snow contain air and are therefore 
whitish and opaque. 

Farther down, the surface is traversed with irregular 
wave-shaped ridges, and finally it becomes a field of hum- 
mocks, half-drowned in streams of muddy water. It ends 
at length in a mountain torrent. 

The ice hummocks are conical in shape and are found at the lower 
end. Not infrequently one or more of them is surmounted by a 
large bowlder. The bowlder protects its support from the heat of the 
sun, while the latter melts the ice around the lower end of the column. 
Sooner or later the ice column breaks and the bowlder falls to a lower 
level, where the same process is again repeated. 



160 



PHYSICAL GEOGRAPHY 



All this mass of ice and snow constitutes a glacier. It 
is in motion and, excepting the imperceptibly slow motion, 
its movements are much like those of a stream of water. 
The flow is faster at the surface than at the bottom, and 
swifter in mid-stream than at the edges. 

Motion of Glaciers. — Because the glacier moves more 
rapidly in the centre than at the sides, the surface is scored 
with cracks and chasms called crevasses. These are roughly 

parallel and cross the 
glacier in oblique lines 
which point upstream. 

This peculiar feature gave 
rise to the opinion that there 
might bean upstream mot ion 
to a glacier. The reason for 
their direction, however, is 
evident; the crack or break 
is necessarily at right angles 
to the direction of the strain. 
The movement of the ice is 
twofold — downstream and 
away from the hank. There- 
fore when the ice breaks the 
crack points diagonally up 
the slope. 




CREVASSES AND MORAINE, NISQUALLY 
GLACIER, WASHING T< >X 



In various cases the 
crevasses form curving 
lines that are like the ripples in a river. Ordinarily, the 
crevasse is narrow and only a few feet deep; bul in some 
places it becomes a chasm fifty or sixty feel in depth. 
Crevasses are most numerous where the slope is the steep- 
est; in general, they mark what in a river would he the 
rapids. 

The velocity of the flow varies. On a gentle slope it may 



WORK OF AVALANCHES AND GLACIERS 161 

not be more than three or four inches a day; on a steep 
incline it may be half as many feet. In summer, when the 
temperature is above the freezing point, the motion is twice 
as great as in winter. 

Moraines. — As the ice stream makes its way down the 
ravine, fragments of rock fall from the banks and lodge 
at the edges. These accumulate until they form walls of 
considerable regularity. These walls constitute the lateral 
moraines of the glacier. If two or more glaciers flow into 
the same ravine, the moraines on the sides that join unite 
to form a medial moraine. Several medial moraines may 
stretch with great regularity a long distance. 
- Toward the lower end of the glacier, much rock waste 
gets to the bottom. In summer, when the lower end of the 
glacier melts, the rock waste, consisting mainly of bowlders 
and gravel, is strewn along the bed. But in winter, when 
the ice front again advances, the scattered material is 
pushed forward, forming the long ridge that constitutes the 
terminal moraine. 

The moraines of a glacier are one of its most interest- 
ing features. Frequently the shape of the ravine is such 
that the rocks of the lateral moraine are pushed against the 
sides, forming walls as regular as though laid by human 
hands. The lateral moraines may decrease in size, but the 
terminal moraine constantly grows in volume. 

Glacial Ice Sheets. — Glacial movements are not con- 
fined to the ice streams of ravines. The sheet of snow that 
projects over the edge of a roof is a perfect illustration of 
glacier motion; and so, too, is the patch of snow on a steep 
hillside that gradually creeps downward or acquires a dis- 
torted shape. 

But there are remarkable fields of ice many miles in 



162 PHYSICAL GEOGRAPHY 

extent, that exhibit the phenomena of glacier movement. 
These are found mainly in polar regions. They are not 
confined in ravines; they are sheets that cover large areas. 
The greater part of the sheet is gradually settling down- 
ward; and the ice in many places is projecting beyond the 
edges of the slope and is breaking off. 

The Greenland ice sheet is a striking example. Almost 
the entire island is covered with ice and snow that have been 
accumulating during long periods of time. So far as known, 
the only rock that reaches above the surface of the ice is 
found near the coast, where the ice-covering is thinnest. 

Along the southern coast much of the ice and snow dis- 
appear by melting. Farther north, however, the ice de- 
scends into the fjords, sometimes presenting an unbroken 
wall several miles in extent. In places the flow of the ice 
sheet is comparatively rapid — as much as forty feet a day. 

Humboldt Glacier, on the west coast of Greenland, is a 
striking example of the ice sheet. For about sixty miles, 
its ragged front, broken here and there by rock cliffs, forms 
a sea wall several hundred feet high. The most stupendous 
ice sheet is in antarctic regions, where it is more than 
half a mile in thickness. 

Icebergs. — The fragments broken from the ice front of 
glaciers that reach the sea are icebergs. Some tumble from 
the top; most commonly, the edge of the glacier is pushed 
out into the water and the buoyant force of the latter breaks 
off fragments. The formation of icebergs along the sea- 
front of glaciers becomes an important factor in several 
ways. The icebergs from the west coast of Greenland float 
southward and during May and June cross the routes of 
transatlantic steamships, thus becoming a menace to 
navigation. Several hundred of them at times drift about 



WORK OF AVALANCHES AND GLACIERS 163 

in the vicinity of the Newfoundland Banks, and remain 
there until they melt or are broken up by storms. 

The huge blocks broken from the Antarctic ice sheet drift 
about over a very large area, sometimes being found as far 
north as latitude 40° S. In the North Pacific Ocean the 
icebergs are small and are rarely found beyond the partly 
enclosed waters of the Alaskan coast and Bering Sea. 




BIRTH OF THE ICEBERG 
The buoyant force 0} the water is breaking ofj fragments, and the latter float away. 

Occurrence of Glaciers. — In general, glaciers begin 
above the line of perpetual snow and extend a short distance 
below it. In low latitudes they rarely occur below the 
altitude of fifteen thousand feet, while in polar regions they 
may flow into the sea. 

The largest stream glaciers known are in the Himalaya 
Mountains; the best known are those of the Alps. Along 
the northern coast of Norway there are fine examples; in 
the Patagonian Andes, and along the Alaskan coast, almost 
every arm of the sea contains one or more of them. In the 



164 



PHYSICAL GEOGRAPHY 



Rocky Mountains there are numerous glaciers, but none of 
them is of great size. Several of the glaciers of Mounts 
Shasta and Tacoma (Rainier) rival the Alpine ice streams 
in extent. Muir Glacier, Alaska, has a frontage of two 
miles on the sea. 

Most of the rivers flowing from the slopes of mountains 
that reach above the snow line have their sources in glaciers. 

Physiographic Effects of Glaciers. — The results of 




REGION OF GLACIATION IN THE UNITED STATES 

The heavy line shows the limit of terminal moraines: erratic bowlders and small areas oj drijt 
occur in occasional localities a liltle farther south oj the line. 

glacial action are readily observed in the glaciers of the 
present time. They are full of character and form an 
excellent key to study those of prior geological times. 

The chief effects of glacial action are erosion and trans- 
portation. Ice is so soft that it has little or no wearing 
effect on hard rock, but if a moving mass of ice drags 
fragments of rock at the sides and bottom, it becomes a 



WORK OF AVALANCHES AND GLACIERS 165 

cutting tool of great power, planing, gouging, or scratching, 
according to the character of the rock which it thus holds, 
and over which it moves. 

All through the northern United States and Canada, 
westward to the Pacific, the surface has been scoured by 
glacial ice. Many thousand lake basins have been made or 
shaped by it. In New England and New York, the grooved 
and rounded surfaces of the rock are a marked feature, and 
everywhere the erosion reveals its origin. The northern 
Appalachian Mountains were worn and broken, and the 
wide gap between the Adirondack and Catskill ranges 
was probably made during the glacial epoch. That the 
surface of the ice sheet did not reach quite to the top of the 
highest peaks of the Adirondack and White Mountains 
is inferred from the fact that certain alpine species of 
plants, still found at their summits, do not occur at a lower 
level. 

The same markings are equally plain throughout north- 
ern Europe, and the coasts of Norway and the British 
Isles probably received their present frayed and ragged 
appearance at the time when so much of North America 
was covered with glacial ice. 

The Transportation of Drift. — The transportation of 
material is a still more noticeable effect of glaciation, and 
the rock waste that has been removed is commonly known 
as drift. Glacial drift is unsorted material, the pieces 
varying in size from grains of sand to bowlders weighing 
many tons. The character of the drift differs materially 
from that of stream gravel; for while the latter is composed 
of uniformly rounded pieees the fragments of the former are 
quite as apt to be rough and angular, with one or more 
faces planed smooth. 



166 



PHYSICAL GEOGRAPHY 



Glacial rock waste or detritus has been deposited in various forms. 
Much of it has been spread over the surface as an imperfectly mixed 
mass of clay, sand, and gravel. These deposits are the well-known //// 
plains of northern Europe and the United States. Sometimes the 
material takes the form of rounded hills of considerable size, called 
drumlins. These are normally heaps of clay and irregular bowlders, 
and usually they occur in groups or clusters. They are common in 
New England, New York, and the region about the Great Lakes. Sev- 
eral of the islands in Boston harbor are drumlins. In many places 
the waste has been spread out in the form of a long, winding ridge, 
which extends for miles in the direction which the ice sheet apparently 
moved. These ridges, called eskers, are common in New England and 
the southern part of New York. It is thought that they were formed 
by streams of water that had forced a passage under the ice. Irregu- 




A DRUMLIN 

In many instances the surface is covered with fertile soil. 



lar clusters of gravel heaps, the material being usually stratified, are 
also of common occurrence. These heaps are smaller in size than 
drumlins, and contain little or no clay and large bowlders. They are 
known as kames. Sometimes they have the form of low, winding ridges. 
Drumlins, eskers, and kames are common in Europe as well as in Nort h 
America; usually they occur at or near the lower limits of the glaciated 
region. Kettle holes, or bowl-shaped depressions, found where huge 
blocks of ice have melted and left diffusions, are also common along the 
lower limit of glaciation. Kettle holes most frequently occur in ter- 
minal moraines. They shoidd not be confused with the " pot holes," 
which are formed by the grinding motion of rock fragments at the 
bed rock of river channels. 



WORK OF AVALANCHES AND GLACIERS 167 



' ,S5 



At the southern limit of the glacial ice sheet near the 
Atlantic, the drift occasionally takes the • form of long 
ridges of bowlders — perhaps many miles in extent, and one 
hundred feet or more in height. In nearly every instance 
these heaps are 
moraines. A 
part of Long 
Island is prob- 
ably a termi- 
nal moraine, as 
also are several 
of the ridges 
that cross New 
Jersey. Many 
of the low 
ridges extend- 
ing into the 
valleys of Colo- 
rado are mo- 
raines. 

The finer drift 
of glaciation has 
been strewn over 
the northern Mis- 
sissippi Valley, 
and now consti- 
tutes the surface 
of the prairie 
plains. There are several strata of this drift, and the material differs 
much in productivity. In the northern part of Illinois a creek marks 
the edge where two areas of drift join. On one side of the stream the 
land is worth about one hundred dollars per acre; on the other side, 
it is worth less than one-half as much. 




SPLIT ROCK: AN ERRATIC BOWLDER 

The bulternid-iree, growing jrom the cleft, is jorty years old. 



A remarkable form of drift is found in the rounded 



168 PHYSICAL GEOGRAPHY 

blocks of stone strewn over the surface of the New England 
and Middle Atlantic States. These are commonly known as 
erratic boivlders. In mineral character the bowlders are of 
many kinds; those of the northeastern United States are 
mainly of granite. The most interesting feature about 
them is the fact that they are unlike the rock in the locality 
where they are found; in some instances they have been 
brought from a long distance. Some of them are of enor- 
mous size; one, Split Rock, near Mount Vernon, New York, 
weighs not far from five hundred tons. 

Many years ago this bowlder broke into two parts along a cleavage 
plane. A butternut-tree grew up in the cleft and in time its trunk 
has wedged the two fragments apart in the form of a V-shaped opening. 
In the northern part of Westchester County a huge erratic block has 
been deposited on the top of three smaller stones, the latter forming a 
very firm tripod. In a number of instances a bowlder has been depos- 
ited on the top of a boss of rock in such a position that the equilibrium, 
while more or less unstable, cannot be readily overthrown. Examples 
are found throughout the New England States, and they are popularly 
known as rocking stones. There is a fine example in Bronx Park, New 
York City. Rocking stones are also common in the glaciated regions 
of northern Europe. 

QUESTIONS AND EXERCISES. — Describe any effects you have 
noticed with relation to snowslides on the roofs of buildings or steep 
slopes. 

A mass of snow weighing ten thousand tons moves with a velocity 
of twenty-five feet per second; what is its momentum in foot- 
pounds? Would this force be sufficient to break off or uproot large 
trees? 

In a previous paragraph it is stated that the water issuing from the 
end of a glacier is muddy; account for the presence of the mud. 

Explain the way in which rock fragments may get to the bottom of 
a glacier. Why are the scratches made by these fragments parallel? 

Why are there no glaciers in the Appalachian Mountains? 

The map on p. 164 shows the terminal moraine of the great ice 
sheet; describe its course and location. Name two large lakes situated 
in the basin of former Lake Agassiz. 



WORK OF AVALANCHES AND GLACIERS 169 

Describe any evidence of glaciation in the neighborhood in which 
you live, noting drumlins, eskers, moraines, markings and scratches, 
erratic bowlders, or drift. If possible delineate them on a map. 

COLLATERAL READING AND REFERENCE 

Tyndall. — Forms of Water. 

Tyndall. — Hours of Exercise in the Alps. 

Le Conte. — Elements of Geology, pp. 569-583. 

Hall. — Geography of Minnesota, pp. 54-74. 



CHAPTER X 

THE WASTING OF THE LAND: THE RESULTS OF 

IMPERFECT AND OBSTRUCTED DRAINAGE. 

LAKES AND MARSHES 

In flowing from higher to lower levels along lines of 
least resistance, the water may find its passage tempora- 
rily obstructed, or perhaps wholly blocked by obstacles. 
Sometimes a ridge of land prevents its progress; in other 
cases a landslide or, perhaps, a stream of lava athwart 
the channel prevents its progress. The water therefore 
spreads out, forming a lake, pond, or marsh. In places 
where the flow is obstructed, one of two things must occur 
—either the water will collect until its surface is high 
enough to flow over the lowest part of the rim, or else it 
will spread over the surface until the amount that evapo- 
rates just equals that which flows in. The area whose 
waters flow into the lake constitutes its basin. A large 
basin usually has several rivers and many small streams 
that are its tributaries or feeders. 

Marsh Lakes. — In a region of considerable rainfall, if 
the general slope be very decided, perhaps there may be no 
lakes and ponds, for the reason that the water flows off, 
meeting no obstructions which cause it to collect in basins. 
On the contrary, if the surface be flat, the water, finding 
no definite channels, spreads over the surface and forms a 
multitude of small ponds. In Florida and along the Gulf 

170 



IMPERFECT AND OBSTRUCTED DRAINAGE 171 

Coast there are excellent examples, and they are commonly 
called marsh lakes. 

Marsh lakes are rarely more than a few feet in depth. They are 
seldom navigable, and commercially they are of but little importance. 
In Europe many such lakes have been drained in order to make culti- 
vable land of their beds. There are several instances where such basins 
are filled with water and used for fish culture for a period of several 
years, and then drained and cultivated for a like period. 

Marsh lakes of large size or considerable depth could 
not form in perfectly flat lands, for the reason that the 




MARSH LAKES, FLORIDA 

water would flow off as fast as it was supplied. For a 
similar reason, such lakes could not be very numerous on 
a surface that had a considerable slope. 

Glacial Lakes. — There are many thousand lake basins 
that are the result of factors with which rainfall has no 
direct connection, except to fill the basins after they have 
been made. The most important are those whose basins 
have been shaped largely by the action of glaciers. 



172 PHYSICAL GEOGRAPHY 

A map of the northern part of North America shows 
that the lakes of this region are its most remarkable surface 
feature. As a rule they are long and narrow, and the axes, 
or lines of greatest length, of each are nearly parallel. Care- 
ful investigations have shown that such lakes are com- 
paratively deeper than the marsh lakes previously described, 
and that, in most instances, their basins have been wrought 
in the hardest rocks. In certain instances, such as the 
"walled lakes," their rims consist of walls of bowlders that 
could scarcely have been more regular had the courses of 
rock been laid by human hands. 

Walled lakes are common in Iowa, Minnesota, and Dakota. So 
regular are the walls of their shores that for many years it was com- 
monly believed they were built by a prehistoric race of people. As a 
matter of fact, the walls are the work of ice. In severe winters these 
lakes freeze nearly to the bottom. When the water freezes, the ice 
expanding, pushes the bowlders shoreward. This process has been re- 
peated until the rocks were pushed back to a position where the resist- 
ance of the earth back of them was equal to the pushing force of the ice. 

In many instances glacial lakes occur in chains, a river 
following the course of each chain; indeed, these lakes are 
merely incidents in the history of the river. A cluster of 
such lakes radiates from a central point, as is seen in the 
"finger" lakes of New York. Glacial lakes are closely 
associated with the great accumulation of glacial ice that 
formerly covered a large part of the northern hemisphere. 
The lakes themselves are found in glaciated regions only — 
never elsewhere. In the carving and sculpture of their 
basins, the fragments of rock held in the grip of (he ice 
were the cutting tools. 

Accidental Lakes. — Occasionally, a lake is (lie result of 
accident — such as the destruction of a river loop, (lie dam- 



IMPERFECT AND OBSTRUCTED DRAINAGE 173 

ming of a stream, the formation of a bar across an estuary 
or cove, or the sinking of an area of land. 

In the illustrations pp. 114 and 116 there is shown a 
type of lake that is common along the bottom lands of the 
Mississippi and of other rivers that flow through level plains. 
The origin of such lakes is apparent. They are mani- 
festly the abandoned loops of the river, and they are formed 
when the latter straightens its channel. The moat thus 




GLACIAL LAKES 

A group in the Adirondack Mountains, New York. 



formed remains filled with water. A bayou or small 
stream may remain as a feeder, but sooner or later the 
moat becomes a stagnant pool — possibfy to be overgrown 
by vegetation, or to be buried under the sediment brought 
down by floods. 

Another type of accidental lake occurs along low, flat 
coasts. These are the lagoons of the sea-shore or the lake- 
shore. The south coast of Marthas Vineyard furnishes an 



174 



PHYSICAL GEOGRAPHY 



Chop 
f.Chop 



excellent illustration of lagoons of this type. In times past, 
this shore was a succession of coves and small bays. But 
the water on this side of the island is so shallow that the 

waves, dragging 
on the bottom, 
finally pushed 
enough sand be- 
fore them to 
make barriers 
across the coves, 
and thereby 
shut them off 
from the ocean. 




LAGOONS: MARTHAS VINEYARD 
In the western part is a blocked river. 



Not only have 
coves of the sea- 
shore been shut off, 
or " bottled," by bars, thus forming lagoons, but the same process has 
been carried on along the shores of lakes. Such lagoons are in process 
of formation at the head of Lake Superior, Lake Erie, and Lake 
Ontario. The formation of the lagoon is not always complete, be- 
cause the current from the river may keep a channel open. 

A map of the United States or of Europe will show many 
such wave-formed lagoons. Those nearest the shore are 
sounds rather than lagoons. But as the coast extends 
seaward, many of the lagoons now near the shore will ulti- 
mately be at a considerable distance inland. Albemarle 
and Pamlico Sounds are examples, and they remain as 
sounds for the reason given. In other words the sound is 
often an intermediate stage between a bay and a lagoon. 

.In other instances flowing lava has blocked a river channel and funned 
a lake. In two places the Columbia River was thus blocked, and the 
high-water marks of the lakes formed are still plainly visible. But 
the river succeeded in recovering its channel and the lakes were there- 



■IMPERFECT AND OBSTRUCTED DRAINAGE 175 

fore drained. Accidental lakes, resulting from the blocking of a river 
channel by coulees of lava, are common in volcanic « countries. 

Still another form of accidental lake is the crater lake, which is merely 
an old volcanic crater filled with water. Crater Lake, in Oregon, and 
Lucrine Lake, in Italy, are examples. The former is about 2,300 feet 
deep. 

Salt Lakes. — Salt lakes have no outlets, and they are 
salt for that reason. Nearly all soil contains more or 
less mineral salts that are soluble in water. Even the 
hardest granites and igneous rocks contain some soluble 
matter. So when the water flows to the basi% it carries 
with it the soluble matter with which it comes in contact. 
If the lake or pond has an outlet, both the water and the 
dissolved matter flow off together. If there be no outlet, 
however, the water is removed by evaporation, while the 
mineral salts, which cannot evaporate, remain in the basin. 
In time, the water becomes so saturated that it will dissolve 
nothing more. After this, unless there is an inflow of 
fresh water, the salt sinks to the bottom, and forms also a 
wide margin of crusted salt along the shore. 

In many cases the carbonates of alkaline metals are present in such 
quantities that the waters of the lake are strongly alkaline. Many of 
the lakes of the Great Basin are alkaline. 

Utah Lake overflows into Great Salt Lake through Jordan River, 
and its waters are fresh. Lake Chad, in Africa, is normally without 
an outlet. In seasons of unusual rains, it overflows into the Libyan 
Desert, and this occasional overflew has been sufficient to keep its 
waters comparatively fresh until recent times. 

The waters of the Caspian Sea are moderately salt. On its eastern 
border is a lagoon, the Karabogas, connected with the main body 
of the lake by a narrow strait. The waters of the gulf are very shal- 
low, and so great is the evaporation, that a four or five knot current 
constantly flows into it from the main body of water. From this in- 
flow about 250,000 tons of salt are deposited daily. If this amount 
of salt were left in the lake the latter would become a saturated 



176 PHYSICAL GEOGRAPHY 

brine. But because of this deposit of salt, the waters have not be- 
come materially saltier since measurements have been made. 

Temperature and atmospheric moisture are also factors 
in the origin of salt lakes. High temperature and dry- 
ness of the atmosphere promote evaporation; and doubt- 
less there are lakes now fresh, that would become salt were 
the temperature to increase and the rain-fall to decrease 
materially. 

Although salt lakes have no outlets, it is not necessarily 
true that lakes without outlets are salt. As a matter of 
fact, there are many lakes without outlets whose waters are 
about as sweet and pure as when they fell from the clouds. 
Of this apparent contradiction there are two explanations. 

In the first place the lakes may be young. In this case, 
time only is required to change the fresh water to a salt 
lake. The time will be short if the soil through which 
the feeders flow contains much soluble matter. In the 
second place, all the soluble matter may have been washed 
out of the soil at the time when the lake overflowed its 
basin. There are fresh lakes without outlets in Canada 
and the United States that will so remain for a long time 
unless the conditions of their existence are changed. 

A salt lake may become fresh by drying up. Dviring a long-continued 
period of drought, it may dry up, leaving its mineral salts as a deposit 
upon the bottom. In time the winds cover this saline crust with fine 
soil; and when the lake again begins to fill, its waters are fresh. Pyra- 
mid and Winnemucca Lakes in Nevada are illustrations; their waters 
are comparatively fresh. 

Playa Lakes. — Certain lakes, in arid regions, are periodic 
in character. During the rainy season they may be of con- 
siderable size; they have no groat depth, however, and in 
the dry season their waters evaporate, leaving in each basin 



IMPERFECT AND OBSTRUCTED DRAINAGE 177 

a thick crust of salt. There are numerous small lakes of 
this character in the western part of the United States; 
some of those in southern Russia are of considerable area. 
Lakes of this kind are commonly called playa lakes. Com- 
mercially some of them are important on account of the 
enormous amount of salt they yield. 

Physiographic Aspect of Lakes. — Lakes are the most 
transitory features of the earth's surface. Rivers and the 
various relief features of the earth are seldom entirely 
obliterated; but a lake is almost ephemeral. There are 
various forces constantly at work to destroy it. Physi- 
ographic agents that have no effect on other features of 
the earth may be fatal to the existence of lakes. 

Among them, glaciers are, perhaps, the chief. Glaciers 
have been energetic factors in making lakes; they have also 
been quite as effective in causing their destruction. The 
glacier blocks the channel of a river with ice or with gravel, 
and a lake is formed. Later it may force a passage through 
the obstructions made, and in a little while the lake has 
disappeared. A few old shore marks and, perhaps, a delta 
or two are all that remain. 

Lake Agassiz, a body of water considerably larger than the five great 
lakes, formerly covered a large part of the valley of the Red River of 
the North. The destruction of this body of water was caused probably 
by glacial action. It had several outlets, one of which was the present 
channel of the Minnesota River. " 

The elevation or the depression of a lake bed always 
produces great changes. Such elevation may throw up a 
ridge so as to form a basin for a new lake; depression may 
lower the land at the foot of the lake and destroy the basin 
of an old one. Long before the existence of the lakes 
whose remnants are now found in the Great Basin, a vast 



178 



PHYSICAL GEOGRAPHY 



body of water covered much of the surrounding region. 
But a change in the level of the basin occurred, and this, 
together with probable changes in climate, caused the 
internal sea gradually to disappear. 

This lake preceded the "lakes now in the Basin Region and was older 
than the Uinta Mountains. The bed of the lake seems- to have been 
lowered, and this was probably a factor in its destruction. 




A BURIED LAKE P,ASI\ T 
The basin has been filled with sediments brought into it by the river. 

Rapidly growing vegetation is also a factor in the de- 
struction of lakes. Vegetation has not much effect on 
deep lakes, but it has a great effect on marsh lakes. The 
process is simple: the roots, stalks, and leaves <>f the dead 
plants fill the basin until there is no more room for the 
lodgement of water. The plants begin their growth at the 



IMPERFECT AND OBSTRUCTED DRAINAGE 179 

edge of the lake and spread toward the centre, little by 
little filling the basin. The struggle may be a long one, 
but in the end the vegetation conquers. Buried and 
partly obliterated lakes of this character are common in 
all coast plains and level lands. 

One near Goshen, New York, covering an area of about sixty square 
miles, has disappeared within recent times and most of its former bed 
is now cultivated land — the famous " onion fields" of the State. 

Winds may help in the destruction of a lake, especially 
the lagoons along the sea shore. They merely carry enough 
fine rock waste into the basin to fill it. The rock waste is 
piled upon the windward shore; each new deposit narrows 
the distance between the shores. The former lagoon is 
filled, and the estuary becomes; a part of the coast plain. 

Lake Mceris, in Egypt, was probably destroyed in this way. It was 
situated southwest of the Nile delta and disappeared within historic 
times; but until within a few years its exact position was not known. 
In this region the movement of wind-blown rock waste is incessant, and 
the amount moved in even a few days is enormous. Canals which 
formerly crossed the Isthmus of Suez have been filled by wind-blown 
rock waste, and appearances suggest that the isthmus itself was formed 
chiefly by winds. 

There are other lake-destroying agencies, and though 
their manner may not be apparent, it is none the less 
effective. "Rivers are the mortal enemies of lakes" 
(Gilbert). The stream that flows into a lake carries 
sediments which, little by little, fill its basin. 

At the place where a stream enters a lake, either a delta or a bar 
forms. This is clearly illustrated by the Volga ; by the St. Louis, at the 
head of Lake Superior; and also by St. Clair River, at the head of 
Lake St. Clair. 

The stream that flows out of the lake is equally destruc- 
tive. It cuts away the rim of the basin, lowering the level 



180 



PHYSICAL GEOGRAPHY 



of the lake until the water is nearly or quite drained. 
Many lakes have disappeared, and many are perceptibly 
diminishing in size from this cause. 

A diminution of the rainfall in its basin will eventually 
destroy a lake. The lakes and old lake-beds in the Greal 
Basin illustrate this fact. Formerly Great Salt Lake and 
its scattered remnants covered an area almost half the size 
of Lake Superior. In a former period, the level of the lake 
was nearly one thousand feet higher than at present. But 

subsequent \y, be- 
tween elevation 
of its basin and a 
decrease of rain- 
fall, the lake has 
dwindled to its 
present size. 

In various 
parts of the world 
old shore -lines 
occur high above 
the present sur- 
face of the water. 
In some instances 
they mark the sites of lakes that have ceased to exist ; 
in others, of lakes that are disappearing. In any case, 
they demonstrate the transitory character of lakes. 

The old shore-lines of Great Salt Lake are still strongly marked, and 
have been surveyed along almost the entire circuit of the basin. Old 
shore lines have been found above the present level of Lakes Titicaca 
and Maracaibo — a clover-leaf bay, rather than a lake. Two old shore- 
lines of Lake Ontario have been found in New York, one of which may 
be traced along nearly the whole of the southern shore. Its level lias 
been somewhat warped by a vertical movement. 




LAKE ST. CLAIR 

The mud Hats at the head of the lake are the result oj 
sedimentation. 



IMPERFECT AND OBSTRUCTED DRAINAGE 181 



Many of the 
lakes of the 
United States 
have disap- 
peared within 
recent times. 
Sevier Lake in 
Utah has prac- 
tically ceased to 
exist, and Tu- 
lare Lake, Cali- 
fornia, in thirty 
years has shrunk 
to less than half 
its former size; 
practically it 
has no outlet. 
The finger lakes 
of New York 
have lost a 
measurable part 
of their area in 
the past fifty 
years, and the 
level of Lake 
Erie has been 
materially low- 
ered. The dim- 
inution has in- 
terfered with 
navigation to 
such an extent 




LAKE BONNEVILLE AND ITS REMNANTS 

The area in -white shows the former size of the lake ; the small 
lakes south of Sevier River are practically dry. 



182 PHYSICAL GEOGRAPHY 

that a barrier across the outlet is contemplated in order to 
raise its level. 

There is possibly a lowering of the basin of the Great Lakes on the 
western, and an elevation on the eastern side. Recent surveys point 
strongly to such a movement of the basin. A continuance of this 
oscillation, aggregating twenty feet, will practically close the lower end 
of Lake Erie, and cause an overflow of Lake Michigan into the Mississippi. 

Waves and wind currents affect lake shores in the same 
manner as they alter the shores of the sea. Bars ami 
spits are formed in the same manner; and the platforms 
made along the shores of lakes do not differ materially 
from marine platforms. The old beach of Lake Ontario 
(p. 180), is now the course of a famous highway known as 
the "Ridge Road." 

Geographical Distribution of Lakes. — Lakes occur 
in all parts of the earth, but they are by no means uni- 
formly distributed; about ninety per cent, of them are north 
of the 40th parallel of north latitude. 

With respect to glacial lakes this law holds almost 
universal^ true. The chief exceptions are those found in 
the southern Andes and the high ranges of Asia. Most of 
the glacial lakes are in Europe and North America. In the 
latter division alone there are about one hundred thousand. 
Why are they of rare occurrence in the torrid zone ? 

Salt lakes are confined mainly to regions of deficient 
rainfall. Why are they not common in regions of abun- 
dant rainfall? Most of them occur in the basin regions of 
North America and Eurasia; in the latter region there are 
several thousand. The Caspian "Sea," the largest lake in 
the world, is in this region; its surface is eighty-four feet 
below sea-level. Playa lakes are numerous in regions 
having a level surface and a light, periodic rainfall. 



IMPERFECT AND OBSTRUCTED DRAINAGE 183 



In general, lakes may be 
grouped in systems which 
occupy lines of depression 
on the earth's surface. Two 
such systems are found in 
the Western and three in 
the Eastern Continent. The 
lakes of the Western Conti- 
nent are chiefly in North 
America, and are embraced 
mainly in two systems. The 
largest and most important 
is the belt stretching across 
the northern part of North 
America. 

An arc of a great circle 
drawn from the city of 
Buffalo to Point Barrow 
passes through or near the 
groups that include the larg- 
est bodies of fresh water in 
the world. Another system 
extends from the northern 
boundary of the United 
States southward through 
Mexico and the Central 
American States. Most, of 
these are situated in a basin 
region; describe their drain- 
age and character. 

South America has re- 
markably few lakes. There 




184 PHYSICAL GEOGRAPHY 

are play a lakes along the eastern base of the Andes, but the 
only lake of importance is Titicaca, a large body of water 
near the summit of the Andes. Its surface is 13,000 feet 
above sea-level, and it is the highest large lake in the world. 
Although Lake Titicaca has an outlet, its waters do not 
reach the ocean. 

In the Eastern Continent a wide belt of lakes, situated 
mainly between the 50th and 60th parallels, extends across 
Eurasia. These lakes constitute the great majority in 
number, but they are not important. 

A second belt follows the high mountain-ranges that 
stretch from west to east across the continent. It em- 
braces the glacial lakes of the Alpine and Himalayan folds, 
and the playa and salt lakes of the basin region. The 
largest and most of the important lakes of the continent are 
in this group. A third system in Africa follows the line of 
the great rift and, unlike the other systems, extends north 
and south. Next to those of North America the African 
lakes are the largest bodies of fresh water in the world. 

In one respect the Australian lakes are remarkable — 
almost every one is either a playa or a salt lake. Not one 
of importance has an outlet to the sea. What does this 
indicate with reference to the rainfall of the continent? 

Swamps and Marshes. — In some places the drainage 
waters cannot flow off, but remain at the surface, thereby 
forming swamps, morasses, pocosons, bogs, and marshes. 

It is difficult to draw the line between marsh lakes, swamps and 
meadow lands. The difference is practically one of degree. A lake 
or a shallow lagoon passes through all the intervening stages. 

In many instances the emergence of underground waters to the sur- 
face by percolation causes swamps. The various bolsas on the coast 
plain between Los Angeles, California, and the ocean are formed in this 
manner. 



IMPERFECT AND OBSTRUCTED DRAINAGE 185 

Inasmuch as imperfect and obstructed drainage results 
in marshy ground, it is evident that the latter may be caused 
by many different factors. For instance, the surface of the 
land may be so nearly level that the water cannot run off 
until it has saturated the soil. This is a common occurrence 
in coast plains, and the marsh lakes of Florida are an ex- 
ample. They also occur along the low flood-plains of rivers, 
where they are known as river terrace swamps. Frequently 
such morasses occur at the mouths of rivers, where they 
form delta, or estuary swamps. 

In some instances the accumulation of vegetable matter 
results in swamps. The leaves and twigs of forest growths 
quickly decay if they fall on dry ground; but if the ground 
be wet there may be no complete decay. The vegetable 
matter gradually forms a black slime and a mass of fibrous 
material called peat. The accumulated matter may prevent 
drainage and a swamp may result. Most woodland swamps 
are formed in this way. 

The character of the vegetation is an important factor in 
swamp-making. Several species of sphagnum, a kind of 
moss, are intimately connected with swamps. One of 
these water mosses consists of long, thread-like stems which, 
while dead at one end, are living and growing at the other. 
The dead portions do not decay; they simply accumulate, 
packing tightly like an immense mass of sponge. 

It is well to bear in mind that peat is not a plant, but a condition 
of imperfect decomposition that, under certain conditions, almost all 
vegetable tissue may assume. The softer parts of the tissue have been 
changed to a black slime, or bitumen, a mixture of nearly pure carbon 
and hydrocarbons; the wood fibre remains. It is likely that the in- 
correct popular notion has arisen from the fact that nearly all the peat 
used for fuel is derived from species of sphagnum. 

If, therefore, the ground becomes wet enough for the 



186 



PHYSICAL GEOGRAPHY 



water-loving sphagnum to thrive most likely the area will 
become a swamp. In time a hollow, a pond, .or even a 
marsh lake will be entirely filled with the stems of sphagnum, 
thus forming peat bogs and lacustrine swamps. 




EFFECTS OF VEGETATION 
Swamp vegetation beginning at the shore, is extending outwards. 

Although all lacustrine swamps are old lakes that have been destroyed 
by vegetation, not all of them become peat bogs. In many instances 
the lake is situated north or south of the latitude in which sphagnum 
grows. The peat bogs of Ireland are historic, but they are not more 
extensive than those of the Danube. Peat bogs occur in nearly every 
country in which sphagnum grows. 

If sphagnum once takes growth, a level surface is not 
necessary for the formation of swamps. The sphagnum 
will make its way up a slope of four or five degrees and 
thus form a climbing bog. Such bogs are common in the 
Scandinavian Peninsula, in Nova Scotia and in the New 
England States. 












EFFECTS OF VEGETATION 



Swamp grasses and sphagnum have nearly filled the lake, and a quaking bog has formed 
at the edges. 

Sphagnous growths not only overwhelm shallow ponds 
and lakes, by filling their basins, but they sometimes attack 
deeper waters. If the moss stems cannot find lodgement 
at the bottom of the lake they will float at the surface, 



IMPERFECT AND OBSTRUCTED DRAINAGE 187 

spreading until the surface is covered. The mat of sphag- 
num grows thicker and broader, and is made firmer by 
slimy matter, which results from decomposition. In time 
the surface becomes firm enough to serve as the bed of a 
wagon road, or even a railway. But the surface never 
becomes quite firm, and when a wagon is driven over it, the 
shaking is perceptible. In this manner a marsh lake is 
changed to a quaking bog, or prairie tremblante. 

Quaking bogs are very common in the swamps of th^ South Atlantic 
States. Usually the mat of sphagnum spreads from the margin toward 
the centre, but in many instances patches of the plant accumulate in 
the open water, forming islands. Generally the insular patches are 
attached to the bottom, but sometimes they float, spreading marginally 
until the surface is covered. In California a branch of the Southern 
Pacific Railway was built across a quaking bog. Subsequently, the 
surface caved in, engulfing several cars of a freight train. 

Canebrakes have more or less to do with swamp forma- 
tion. Canebrakes are sometimes associated with swamps 
as a result; as a matter of fact, they are frequently a cause 
of swamps. The roots of the plant, spread below the sur- 
face of the ground in much the same manner as does the 
sphagnum above ground, and the accumulated matter 
finally becomes an impervious mat that almost wholly 
obstructs drainage. 

Coast Marshes. — Coast or salt marshes are destitute of 
water mosses, but they contain other species of vegeta- 
tion quite as effective in the formation of marshes. The 
first step in the formation of a salt marsh is an area of 
shallow, still water. This condition results as soon as a 
sand-bar is thrown across the cove. Along an open coast, 
waves prevent the formation of a marine swamp, but in 
throwing up a bar they make the conditions which are 
necessary for its existence. 



188 PHYSICAL GEOGRAPHY 

The growth of eel grass, a plant with a long, slender blade, 
is the next stage. The eel grass grows rapidly, and the 
half-deca}^ed remains help to fill up the marsh. Bui eel 
grass grows only when covered with salt water. And when 
the decayed vegetation, mixed with wind-blown rock waste 
and the mud deposits of high tides, has filled the cove to 
low-tide level, the eel grass perishes. After a time the 
marsh receives additional layers of sediment that build its 
surface so high that it is awash at high tide only. 

By this time true salt-marsh grasses, reeds, and rushes 
obtain possession. These species thrive best when their 
roots are covered with salt water at short intervals. They 
accumulate until the level of the marsh is built above the 
level of the highest tides. When this stage is reached turf 
grasses gradually take the place of salt-marsh grasses, and 
the marsh becomes meadow land. 

Another plant active in the formation of coast swamps 
is the mangrove tree. This tree thrives only in salt water. 
It propagates itself partly by upshoots from the roots that 
trail under water, and partly by seeds. The spreading of 
mangrove roots and trunks is so great that coast outlines 
are extended. In Florida mangroves and corals are adding 
measurably to the swamp-land surface of the state. 

The tundras of the Arctic coast plain furnish an inter- 
esting example of the combined action of ice, fresh water, 
salt water, and moss. These shores are almost constantly 
covered with ice. Not only are they inundated by tidal 
waters, but also by stream waters. When the mouths of 
the streams are frozen, the flood water, finding its chan- 
nels blocked with ice, spreads over the surface. 

During flood seasons the stream waters are filled with 
sediment, which is spread over the plain. Moreover, the 



IMPERFECT AND OBSTRUCTED DRAINAGE 189 

sediment furnishes sufficient nutriment to heavy growths 
of- coarse moss, and the latter, in turn, not only holds the 
sediment in place, but it also helps to prevent the melting 
of the ice. As a result, this plain is perpetually a half- 
frozen morass. 

Physiographic Aspects of Marshes. — Although the 
area of marsh lands at any one time is comparatively 
small, much of the land surface of the earth has been a 
marsh in some period of its existence. Murine marshes 
may be considered as land at an intermediate stage be- 
tween submergence and elevation. Hence, volcanic areas 
excepted, the lagoon, the eel grass swamp, the mud flat, 
the salt marsh, and the meadow is each, in turn, an inci- 
dent in the final elevation of a body of land above sea- 
level. 

Along the coast of the South Atlantic States one may 
find the lagoons and the eel grass swamps; along the 
shores of the Gulf there are, in addition, very broad mud 
flats. Surrounding New York and San Francisco Bays 
are many square miles of salt-grass and tule marshes; and 
almost everywhere beyond the reach of tidal waters there 
are meadow lands. 

The mud flat stage is the area that is uncovered at low tide. If the 
slope is gentle this belt may have considerable width; and this is seen 
along the coast of the South Atlantic States and the shores of the Gulf. 

The range of fresh-water swamps may not be so great as 
that of marine swamps, but economically the latter are 
quite as important as the marine marshes. Their evolu- 
tion is more complex than the development of marine 
marshes, but in two respects they are alike — namely, 
vegetation makes them and, in the long run, it likewise de- 
stroys them. 



190 PHYSICAL GEOGRAPHY 

Vegetation may, and usually does, create swampy con- 
ditions, but the process of destruction does not differ 
from that of creation. The accumulation proceeds until 
the surface is at a level where the waters may flow off. 

Cultivation destroys swamps, and the process of destruc- 
tion is simple. Most grains and food-stuffs require a com- 
paratively dry soil, and the very act of ploughing creates 
drainage channels in which the water flows off. Where 
ploughing has not been sufficient, ditching and tile-draining 
accomplish the same results. 

But swamps themselves exert a considerable influence 
on vegetation and its distribution. Many species of trees 
and shrubs that thrive in dry soils perish if the soil be 
saturated. Therefore, a swamp once forming in a wood- 
land may destroy much, or even all the forest growth. In 
almost every fresh-water swamp one may find an abundance 
of stumps and trunks of dead trees — a result of the devel- 
opment of swampy conditions. 

Economic Value of Swamps. — Though practically un- 
habitable for human beings, swamps, marshes, and bogs 
have had a very far-reaching effect in the development of 
civilization. In evidence of this the coal beds ma}' be 
cited. The enormous development of commerce and man- 
ufactures is due almost wholly to the coal fields of the 
world, and these almost without exception are products of 
the swamps and marshes of prior geological ages. 

The swamps of the present time will be the productive 
areas of the future. The soil is deep and its nutrient 
qualities are great. Swampland crops are important and 
the rice-swamps probably supply food to a greater number 
of people than all the other grain fields in the world. In- 
cidentally, the world's supply of cranberries comes mainly 



IMPERFECT AND OBSTRUCTED DRAINAGE 191 

from swamps, and the peat bogs furnish fuel to fifty mil- 
lions of people. 

The Movement of Rock Waste. — In this and the 
preceding chapters it has been shown that the higher parts 
of the land are almost everywhere crumbling and wasting 
away under the action of water in one or another of its 
different forms. Rain, snow, ice, running streams, and 
even the winds are factors that are unceasingly active, and 
their legitimate work is to wear away the }and and trans- 
port the waste to sea-level. 

On the steeper slopes, as a rule, the rock waste is coarse, 
the fragments sometimes weighing many tons. On its 
way downward it is broken and worn in various ways 
until, at sea-level, it is very fine. Much of it is also min- 
gled with the remains of vegetation, and becomes soil. 
The latter is deposited in river valleys and becomes a part 
of the structure of flood-plains, delta-plains, estuary plains, 
and coast plains. Some of the waste, temporarily re- 
tarded along its downward journey, fills depressions, and 
forms lacustrine plains; and all of these are factors not 
only in economic history, but in political history, as well. 

The waste of the old land is the material of the new. 

QUESTIONS AND EXERCISES. — Study any lake or pond near 
which you live and classify it as marsh, glacial, swamp, or salt; 
make a map of it. 

Note whether a coast plain is present, or whether the water-level is 
at the foot of cliffs or banks. 

If there is a fringe or belt of coast plain what does it indicate con- 
cerning the present and the former size of the lake? 

Note whether or not the border is marshy and thickly covered with 
vegetation, or whether it is strewn with large bowlders. 

In what, if any, part are the waters muddy? From this determina- 
tion endeavor to find where the sediment is chiefly deposited. 

From the foregoing write a description of the body of water. 



192 PHYSICAL GEOGRAPHY 

From the profile of the Great Lakes, together with a good map, 
p. 183, prepare a description of these lakes. What will be the effect 
of the recently completed ship canal at Chicago, on the level of Lake 
Michigan? 

What would be the effect on the character of the water were the 
basin of the Caspian Sea to fill until it overflowed? 

If the basin of the Black Sea were elevated twenty or thirty feet 
what would the water be, salt or fresh? 

Mention some of the benefits resulting from the Great Lakes of 
North America, with reference to commerce, industries, and climate. 

Which of the two Great Lakes may be regarded as a single body of 
water? Why? 

The level reach of land in the illustration, p. 178, was formerly a 
lake ; explain how it became the flood-plain of a mountain stream. 

From any convenient source of reference write a description of 
Death Valley, or of the Dead Sea, Syria. 

From the map of the marsh lakes, p. 171, prepare a description of 
them, concerning their depth, altitude, and navigability. 

COLLATERAL READING AND REFERENCE 

Russell. — Lakes of Nevada, Physiography of the United States, 
pp. 101-130. 

Le Conte. — Elements of Geology, pp. 80-82, 580-581. 
Shaler. — U. S. Geol. Survey, An. Rep't, 1800. 
Hall. — Geography of Minnesota, pp. 109—220. 



CHAPTER XI 

OCEAN WATERS AND THEIR MOVEMENTS: WAVES, TIDES, 
AND CURRENTS 

Almost all the phenomena connected with the wasting 
of the land, with climate, and even with the existence of 
life, in one way or another depend on the sea. In at least 
two ways the sea differs from other bodies of water. It 
is many thousand times the size of the largest body of 
fresh water and, two or three inland lakes excepted, its 
surface level is lower. The sea supplies the land with 
fresh water, and because of its lower level, almost all the 
waters of the land sooner or later flow back into it. 

Sea water is briny and bitter; doubtless it has always 
been thus, but inasmuch as the stream waters flowing into 
it are constantly dissolving mineral matter from the rock 
waste and carrying it to the ocean, the amount in the latter 
is constantly increasing. Every one hundred pounds of 
sea water, on an average, contains about three and one- 
half pounds of saline matter; most of this is common salt, 
the remainder being chiefly lime and magnesia. The per- 
centage of mineral matter varies. In localities where 
evaporation is rapid, the proportion of salt is larger. 
Thus, in the Red Sea it is more than four per cent., while 
in the Baltic Sea it is less than one-half as great. It is 
somewhat greater in tropical than in polar regions. 

Bulk for bulk, sea water is heavier than fresh water. A 
cubic foot of fresh water weighs about 1,000 ounces; on 

193 



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III II III! 






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111 

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^iiljiil'li'i! |' ' " 







WAVES, TIDES, AND CURRENTS 195 

account of its mineral matter the same volume of sea 
water weighs at least thirty-five ounces more. Tempera- 
ture also affects the density of water; if 1,000 cubic inches 
of water at the freezing-point be heated to the temperature 
of a hot summer day, its volume will be increased seven or 
eight cubic inches. The differences in temperature and 
density have far-reaching results; for upon these varia- 
tions the general circulation of the waters of the sea in 
part are due. 

The temperature of the sea varies with both latitude and 
depth. In general, the surface waters of equatorial re- 
gions are warmest, and in the broader extents of the sea 
their temperature is not far from 26° (79° F.). Toward the 
poles it gradually falls, and in polar regions it is rarely 
much above the freezing-point. The variation of temper- 
ature with latitude is by no means uniform, however, for 
in various places warm water dragged by the "skin fric- 
tion" of winds is frequently found in high latitudes. 

With relation to depth the variation is remarkably uni- 
form. In low latitudes the bottom temperature of deep 
water is a degree or two above the freezing-point of fresh 
water; in polar latitudes, a degree or two below it. In 
shallow waters and land-locked basins, however, the varia- 
tions in temperature are usually very irregular. Thus, the 
entrance to the Gulf of Mexico is blocked by a submarine 
ridge whose crest is 1,200 feet below the surface, and be- 
cause of this, water whose temperature is lower than that of 
the 1,200-foot level cannot enter the Gulf. But even at a 
depth of 12,000 feet, the temperature varies but little from 
that of the 1,200-foot level. 

The freezing temperature of salt water is lower by two 
or three degrees than that of fresh water, the difference 



196 



PHYSICAL GEOGRAPHY 



depending mainly on the amount of mineral salts in solution. 
The ice of the sea is therefore formed in high latitudes, 
where the temperature is much below the freezing-point. 

Bulk for bulk, ice is lighter than water. Solid sea ice 
floats with about one-eighth of its mass above the surface. 
It it contains air bubbles, however, a greater proportion is 
out of water. 

Sea Ice. — Sea ice takes various forms. The nearly level 
and narrow shelf that in polar regions forms along the 




ICE OF THE SEA: FLOE, PACK, AND BERG 

shore, and skirts almost its entire extent, is called the ice 
foot. Any considerable extent of undisturbed or unbroken 
ice forms an ice sheet or ice -field. When on-shore winds 
become so strong that the ice field is crushed and piled up 
against the shore, it forms pack ice. Detached masses 
floating about constitute floes; finely broken ice floating 
on the surface is called sludge. 



WAVES, TIDES, AND CURRENTS 197 

The formation of pack ice is sometimes sudden and frequently violent. 
The crunching from side pressure, due to the friction of the wind, is so 
great that not only is the ice piled up in huge blocks, but the blocks, 
often weighing many tons, are shot up into the air ten or twenty feet. 

Anchor ice results from the freezing of fresh water at the bottom 
of an estuary into which salt water flows. The ice accumulates on the 
bottom until its buoyancy overcomes the force with which it adheres to 
the bottom; then the whole mass rises to the surface. It receives its name 
from the fact that it is very apt to begin forming about anchors or other 
metallic substances lying at the bottom. Not infrequently these have 
been lifted from the bottom and floated. Large areas of anchor ice 
at times are suddenly detached from the bottom, and the estuary, 
previously free from ice, becomes filled with sludge. This form of ice 
is called ground ice. 

Some of the glacial ice, in the form of icebergs, is carried 
by currents or blown by winds, into warmer latitudes, 
there to melt, but by far the greater part, however, never 
leaves polar regions. Some may accumulate, but much of 
it melts during the brief polar summer. 

The difference in the form of the Greenland and the south polar 
icebergs is due to the character of the glaciers from which they are 
broken. Antarctic icebergs are derived from sheets of land ice; Green- 
land bergs, on the contrary, are derived mainly from the hummocky 
ice of glaciers. Most of the icebergs floating down through Davis Strait 
come from Disko Bay. 

Waves. — Waves vary in size from the tiny ripples made 
by a summer breeze, to the huge billows that toss the largest 
ships. Waves are caused by the friction of the air against 
the surface of the water. The motion of the water of the 
wave is up and down, combined with a rotary movement. 
Under a strong wind, however, the top of the wave is pushed 
forward and, if the gale be very strong, it breaks into foam, 
forming white caps and scud. Before the strongest storm 
winds much of the water is blown into spray, and the 
whole surface of the ocean becomes covered with foam. 



198 



PHYSICAL GEOGRAPHY 



When waves roll in upon a shallow coast their motion 
is also modified. The moment the bottom of the wave 
touches bottom it begins to drag. The top of the wave 
not being impeded, advances more rapidly, and finally 
combs, or falls forward, making breakers. The water and 
foam that flow upon the shore constitute the surf. 




STORM WAVES: SURF BREAKERS 

The distance from the shore at which waves begin to 
comb depends partly on the depth of the wave, and partly 
on the depth of water along the shore. Ordinary waves 
rarely exceed three or four fathoms in depth, and therefore 
do not comb until they are within a few rods of the shore. 
Along certain shores of the Indian Ocean, where the coast 



WAVES, TIDES, AND CURRENTS 199 

waters are shallow and the waves are deep, the latter may 
begin to comb at a distance of three or four miles from 
shore. 

For the formation of the highest and largest waves, a 
deep, open sea is required. In calm weather, the waves of 
the open sea are from six to ten feet in height; their breadth 
is about ten times the height. 

With a wind of twenty or thirty miles an hour, the 
height of the wave is increased, and the largest steamships 
pitch considerably as they ride over them. With the wind 
at sixty or eighty miles the breadth of the wave is about 
two thousand feet; its height may reach twenty or thirty 
feet, and its progressive motion may reach forty miles an 
hour. 

Waves do not run highest when the wind is at its maxi- 
mum velocity; they do not reach their greatest height until 
the lull of the wind ; then they sometimes roll to a height of 
forty-five or fifty feet. A very high wind pushes their 
crests forward rapidly, practically flattening them. 

In navigation, the chief damage from storm waves is 
due to the battering of the lighter woodwork above deck. 
In recent years the old custom of spreading oil on the sur- 
face to the windward has been revived. The oil spreads 
quickly and forms a covering or " skin," on water that offers 
comparatively little friction to the wind. As a result the 
waves, although rolling high, no longer break upon the 
vessel, and the latter is enabled to withstand storm waves 
that otherwise would be destructive. 

A stanch vessel with her head to the wind needs to fear but little from 
the waves. The waves may smash everything above deck, but the hull 
will ride them safely so long as they do not board her. If the waves 
strike broadside, however, the case is more serious, and the boarding 



200 PHYSICAL GEOGRAPHY 

waves may cause the ship to founder. Head on, a vessel can ride waves 
of twenty feet as safely as those of six. 

In the use of oil the problem before the sailing master is to prevent 
the breaking of waves. For this purpose it is found that sperm oil 
and oil of turpentine are the best. The oil is poured into a coarse 
canvas sack filled with tow, and the latter is floated to the windward 
of the vessel, being held in position by any convenient outrigging. The 
oil oozing through the canvas spreads rapidly over the surface of the 
water. The friction of the wind against a surface of oil is so much less 
than against a surface of the water that at once the waves cease to break. 

The following from the log of the Swedish brigantine Draft is one of 
many similar testimonials gathered by the United States Hydrographic 
Office: "I had seen upon the pilot chart that oil had been used with 
good effect in calming heavy seas. I started to try it and had two 
bags made of the capacity of two gallons each. These bags were 
stuffed full of oakum, and then one gallon was poured into each, half 
fish oil and half petroleum. A very small hole was cut in the bottom 
of each bag which allowed the oil to drop out freely. One of these 
bags was suspended from each cathead, just out of the water, and the 
result was simply a wonder to me, so much so that I could hardly l>elieve 
my senses. No more seas were shipped and all hands turned to secure 
the main hatchway properly, which was impossible to do before on 
account of the risk of being washed overboard. The former combers 
were now great rollers only, not a sea breaking nearer than thirty feet 
from the vessel. The crew were now able to pump out the ship and 
clear up the decks in perfect safety. About 11 p.m. the sea broke 
over the starboard side and smashed in one of the boats, but this was 
found to be due to the loss of one of the oil bags, and as soon as another 
was put out and kept supplied with oil no more waves came on board." 

The force with which waves strike an opposing surface 
is very great. On the coast of Scotland, measurements 
show that calm-weather waves may strike with a force of 
six hundred pounds per square foot; the momentum of the 
heaviest storm waves is about ten times as great. 

Notwithstanding their tremendous energy, waves are 
superficial. The effects of calm-weather waves do not 
extend more than a few fathoms; the fiercest storm waves 
do not reach more than two hundred feet below the surface. 



WAVES, TIDES, AND CURRENTS 201 

Tides. — The alternate rise and fall of the sea twice a day- 
is familiar to everyone who has visited the sea shore. For 
six hours the level of the water gradually rises, spreads 
over the shore and fills the river estuaries. For a few mo- 
ments, the water is stationary; during the next six hours 
it falls — ever repeating, never ceasing its oscillations. Nei- 




THE TIDE WAVE: MOON IN CONJUNCTION 

ther the high nor the low water level varies much at any 
one place. As the level rises and the water flows in upon 
the shore, the tide is flood; as it recedes it is ebb; its highest 
level is high water, and its lowest, low water. During the 
few minutes at the turn of the tide it is slack water. 

This movement of the water is practically a wave several 
thousand miles broad. Both the sun and the moon at- 




THE TIDE WAVE: MOON IN OPPOSITION 

tract the earth. The solid portion of the earth does not 
perceptibly bend or yield, because it is rigid; the water 
envelope, on the contrary, is drawn into the elongated 
form (Appendix, Table VI), giving the appearance of two 
wave-crests, one on each side of the earth. No matter 
whether the sun and the moon are on the same side, or on 




THE TIDE: MOON IN QUADRATURE 



202 PHYSICAL GEOGRAPHY 

opposite sides, their combined attraction will produce the 
same results. If, however, they pull at right angles, 
four tide waves will be formed — two of the sun and two 
of the moon. 

In much of the Northern Hemisphere, where the con- 
tinents interrupt the tide waves, the solar tides arc merg< x 1 

into those of the moon. 
Only in the broader 
expanses of the ocean, 
among the islands of 
the South Pacific, are 
they distinguishable. 
At new and full moon, 
the pull is exerted in a 
straight line; the tides are then materially higher at flood 
and lower at ebb than when the two are pulling at right 
angles. The former are spring tides; the latter neap tides. 
As the moon revolves around the earth, the waves are 
dragged after it as though they were fastened to it. Each 
wave makes the circuit in about twenty-eight days. 

But while each wave is making its revolution, the earth 
at the same time is turning on its axis, every twenty- 
four hours. The daily motion of the tides, therefore, 
results from the earth's turning on its axis. Every point on 
the earth, accordingly, overtakes and passes the two waves 
daily, very much as though it were slipping under them. 
If the surface of the earth were covered with a uniform 
depth of water, the direction of the tide waves would be 
nearly east and west. As a matter of fact, the position of 
the continents prevents any such uniform direction. Every 
mass of land is an obstacle in the path of the advancing 
wave, and the latter cannot sweep over a continent. 



WAVES, TIDES, AND CURRENTS 



203 



Only in the open waters of the Southern Hemisphere 
do the tides move in their theoretical direction from east 
to West. In the North Atlantic the wave is turned to the 
northward, and, entering the Arctic Ocean, it is diverted 
to the eastward. At Lady Franklin Bay, northwest of 
Greenland, explorer Greely observed that the tide came 
from the north. 




CO-TIDAL LINES 
The lines show the position oj the crest of the tide wave jor each two hours. 

The height of the tides is also affected by the land 
masses. In mid-ocean the difference between high water 
and low water is scarcely three feet. Along the coast of 
the United States it varies from four to ten or twelve feet. 
From New York to Savannah spring tides are about five 
feet, and neap tides about four feet. In the Gulf of 
Mexico the rise and fall is only about one-half as great; 
along the Maine coast it is ten or twelve feet; and at 
Sitka, Alaska, from twenty to thirty feet. 



204 PHYSICAL GEOGRAPHY 

the tides is due chiefly to the shape of the shores. If the 
tide wave faces a V-shaped estuary the advancing body 
is compressed by the narrowing shores. Not being able 
to spread sideways, it is therefore increased both in depth 
and velocity. In the Petitcodiac River, at the head of 
the Bay of Fundy, the tide enters in the form of a rolling 
wave at times nearly six feet high. The advance of the 
tide in the form of a wave is called a bore. It is a marked 
feature in the Amazon, the Seine, and in several rivers of 
the China coast. It is also noticeable in many of the 
estuaries of the British Isles. The spring tide in Bristol 
Channel is sometimes forty feet high and the bore is four 
or five feet in height. 

If the waters of the advancing tide are separated by an 
island lying near the shore, again uniting in the strait 
between the mainland and the island, races and danger- 
ous whirls are formed. Thus, at Long Island the ad- 
vancing wave is divided, one part entering New York 
Bay, the other, Long Island Sound. The two currents 
meet in the narrow Hell Gate, which has been strewn with 
wrecked vessels. The Maelstrom, an eddy formed off the 
coast of Norway, is a similar current. 

In pleasant weather the eddy of the Maelstrom is hardly noticeable 
during slack water, or at the time of neap tides. When the flood 
or the ebb of spring tides is strong, the current also is strong; with a 
hard northwest wind, it is a dangerous locality. 

Ocean Currents. — The sea is .traversed by currents that 
flow in definite directions with a fairly uniform velocity. 
As a rule, the water of an ocean current has an energy of 
its own, and its motion is practically the same as though 
it were flowing from a higher to a lower level. In certain 
instances, however, the movement is caused almost wholly 



206 PHYSICAL GEOGRAPHY 

by the wind. The direction of such a current is due to the 
wind; such wind-blown waters are called drifts. 

Currents are deep, sometimes extending to the bottom; 
drifts, on the other hand, are superficial. A current may 
become a drift, and a drift ma}' become a current. 

The winds, and the unequal heating of the waters in 
equatorial and polar regions are thought to be the main 
causes of the general movement of ocean waters; the 
winds and the rotation of the earth on its axis are the 
chief factors in making them currents and in determining 
the direction of their flow. 

According to Herschel and Carpenter the winds are the chief agents 
in piling the waters in equatorial latitudes, thereby bringing about a 
condition of inequilibrium. Lieutenant Maury held that the difference 
in specific gravity between the saltier waters of equatorial and the 
fresher waters of polar regions is competent to account for ocean cur- 
rents. That each is an important factor cannot be denied. 

In equatorial regions the water receives the vertical rays 
of the sun and is heated. Being heated, it is also expanded 
and flows toward polar regions. At the same time, cooler 
water flows toward the equator in the form of an under- 
current. Thus a constant circulation is taking place — 
a surface movement from equatorial, and an undercurrent 
from polar latitudes. This general movement is modified 
by the winds and by the rotation of the earth. 

Owing to the turning of the earth on its axis, a point on the equator 
travels 25,000 miles in twenty-four hours — a speed of about 1,000 miles 
an hour. In latitude 60° the speed is only half as much. Consequently 
water which flows from latitude 60° toward the equator has a tendency 
to lag behind as it reaches a latitude when the speed of ratal inn is greater. 

In equatorial latitudes the prevailing direction of the 
wind is toward the west, and this gives the waters a west- 



WAVES, TIDES, AND CURRENTS 207 

erly movement. A flow of water, nearly 1,000 miles broad, 
called the Equatorial Current, is the result; except the places 
at which it is interrupted by the continents, it girdles the 
earth. Its flow is scarcely more than a drift, and its rate 
is about ten or fifteen miles per day. Most of the warm 
currents of temperate latitudes are branches of it. 

The Atlantic part of the Equatorial Current is divided 
at the eastern angle of South America. The southern 
branch flows along the eastern coast of this grand division 
for nearly 2,000 miles; what is its name? Gradually it 
becomes a drift, and finally it returns to the Equatorial 
Current. Describe the course of the northern branch. As 
it emerges from the Caribbean Sea and gathers off the 
Florida coast it becomes the Gulf Stream. The Pacific 
part of the Equatorial Current is more than 9,000 miles 
long. At the edge of the Eastern Continent it is again 
divided; what is the name of the northern branch? of the 
southern ? 

In the midstream of the Equatorial Current is found a narrow belt 
of water flowing in the direction opposite to that of the main stream. 
It is called the Equatorial Counter Current ; no satisfactory explanation 
for it is known. 

The Gulf Stream is by far the most important of the 
currents of the Atlantic Ocean. A part of its volume flows 
through Santarem Channel; a greater part is gathered into 
Yucatan Channel; a small but measurable part is drawn 
from the Gulf of Mexico. These branches unite in Florida 
Strait, and here the current begins. 

At Florida Strait its velocity varies from three and one- 
half to five and one-half miles an hour. To the north- 
ward the velocity decreases until, off the Labrador coast, 
it becomes a drift dragged by westerly winds. 



208 PHYSICAL GEOGRAPHY 

The velocity varies not only with the season, but also with the 
passage of the moon — that is, the variations are yearly, monthly, and 
daily. Its flow is swiftest during summer and slowest in winter. An 
adverse wind will retard; a favorable wind will increase its velocity. 
A quartering wind or one blowing athwart is apt to push some of the 
surface water out of the track of the stream, at the same time pushing 
colder water into it. The fact that Gulf Stream water is occasionally 
pushed against the Atlantic coast has given rise to the statement that 
the position of the stream itself is subject to change. 

The Gulf Stream is a very warm current. Off the Florida 
coast its summer temperature is 30° (86° F.), and even near 
the Greenland coast its drift is twenty or thirty degrees (F.) 
warmer than the surrounding waters. It is not a shallow 
current; from Florida Strait to Cape Hatteras, it extends 
to the bottom of the ocean. Its drift is pushed northward 
and eastward, but much of it forms a circuit returning 
to the Equatorial Current. A considerable volume, keep- 
ing northward, finds an entrance to the gulfs and bays 
of western Europe, reaching even to the north coast of 
Norway. 

The Kuro Siwo is the Gulf Stream of the Pacific. Some 
of its waters issue from the Bay of Bengal, but the greater 
part of its volume passes among the Malaysian Islands 
and thence along the east coast of Asia. Off the Japan 
Islands it becomes a drift, and its waters are dragged by 
the prevailing winds toward the North American coast. 
Some of the drift makes an oval-shaped circuit like thai 
of the Gulf Stream; a part is blown northward to the 
Alaskan coast. 

The Kuro Siwo is a much feebler and colder current than 
the Gulf Stream. Its summer temperature rarely exceeds 
22° (72° F.), and its winter temperature is not far from 
17° (63° F.). In summer it extends as far north as the 
Kuril Islands; in winter it scarcely reaches the Japan coast. 



WAVES, TIDES, AND CURRENTS 209 

No part of the Kuro Siwo enters the Arctic Ocean through Bering 
Strait. The prevailing movement in Bering Strait is a feeble flow from 
the Arctic Ocean. 

Much of the circulation of the colder ocean waters takes 
the form of undercurrents, but no complete survey of an 
undercurrent has been made. Two very definite cold 
currents have been observed and their position is fairly 
well known. These are the Arctic Currents. One flows 
southward along the east shore of Greenland; the other, 
flowing on the west shore, emerges into the Atlantic and 
meets the Gulf Stream off Newfoundland. 

Off the coast of Cape Hatteras, almost in the track of the Gulf Stream, 
is an adverse current known on pilot charts as "Little Hell." It is 
marked by heavy, choppy waves, and persists, even in the face of a 
strong southerly wind. Its waters are cold, and it is thought to result 
from the rising of an arctic undercurrent to the surface. 

The Antarctic Current is the chief cold current in the 
southern hemisphere. It is a drift rather than a definite 
current, and its waters are several degrees cooler than those 
with which they finally mingle. 

Economy of Ocean Currents. — One of the important 
effects of marine currents is the equalizing of the tempera- 
ture of ocean waters. Without this interchange the heat 
of equatorial waters would sooner or later become fatal to 
many forms of life, and the polar ice caps would intrude 
far into temperate latitudes. 

The more practical effects are seen by comparing the 
coast of Labrador with that of the British Isles, in the 
same latitude. The harbors of the former are blocked with 
ice for five months of the year; those of the British Isles 
are open the year round. The former is bathed by cold 
waters; the latter by the drift of the Gulf Stream. The 



210 PHYSICAL GEOGRAPHY 

port of Hammerfest, situated within the Arctic circle, is 
free from obstructive ice all the year round. It is doubtful 
if warm currents have any material effect on the tempera- 
ture of a region at any great distance inland, but they keep 
the coast free from ice. How does this affect commerce? 

Evaporation is very great along warm currents and the 
moisture borne with the wind adds much to the rainfall of 
the nearby regions. Cold currents have a chilling effect on 
the air, and if the air has much moisture it is apt to take 
the form of fog. This is notably the case off the Banks 
of Newfoundland, where the Gulf Stream drift meets the 
"cold wall," and the dense fogs of the Newfoundland and 
Labrador coasts are due to this cause. Ocean currents are 
thus indirect factors in climate. 

Sargasso Seas. — Within the ovals formed by the 
branches of the Equatorial Current and their drifts there 
are extensive accumulations of marine plants. These were 
named by Spanish navigators Zargazzo, or grassy seas. 
The accumulations are sometimes attributed to the eddying 
motion of the current and its drift, but such a theory is 
not necessary to the explanation of their presence. Calm 
water is necessary for the growth of the species forming 
such accumulations, and the latter occur most frequently 
in such localities. 

Physiographic Effects of Oceanic Movements. — So 
closely related is the work of waves, tides, and currents, 
that their physiographic effects cannot well be separated 
from one another. In general, the work of waves is both 
destructive and constructive — they not only batter down 
coasts, but they build them as well. On the other hand, 
the work of tides and currents is mainly transporting— they 
carry material from one place to another. Although waves 



WAVES, TIDES, AND CURRENTS 211 

act at the surface, their work is none the less effective. 
Throughout the whole extent of coast material is either 
being removed from the shore or else is being added to it. 

Along the South Atlantic coast of the United States, the 
effects are still more noticeable. The shores of Cape May, 
New Jersey, are wasting away at the rate of several feet a 
year, and those of Charleston Harbor require almost con- 
stant repair, so destructive is the incessant battering of 
the waves. On the east coast of England, owing both to 
waves and swift tidal currents, the yearly waste is con- 
siderable (p. 55). 

On the Sicilian coast is a spectral rock detached from the shore, 
rising almost like a lighthouse tower. Breaking waves have battered 
a hole through it near the top, forming a giant eye — and Cyclops to this 
day is represented with one eye (p. 53). 

Along the west coast of Scotland, and especially among 
the Hebrides Islands, many thousand rocky islets rise 
from the sea like watch-towers. They are witnesses of 
the destructive force of the waves. 

The constructive and building power of waves is finely 
shown along the South Atlantic and Gulf coast and that 
of the Netherlands. The noticeable feature is the multi- 
tude of spits, barrier beaches, and islands that border it. 

In the building of shores much depends on the direction 
of tides and local currents. If the latter strike the shore 
broadside, or at right angles, the bars and spits take the 
shape so common along the Gulf coast; if they strike it 
obliquely, the sediment is caught in the swirl of the current, 
and deposited in the form of sandy hooks. 

Cape Cod, Monomoy Point, and Nantucket Beach are nothing but 
sandy hooks; Marthas Vineyard and Nantucket Islands contain half 
a score of such examples. Sandy Hook, now an island obstructing 
the navigation of New York Bay, is a striking example. 



212 PHYSICAL GEOGRAPHY 

Certain effects of tidal currents al first, are not obvious. 
Waves are capable of battering down a cliff, but they are 
not able to remove the rock waste. This, Lodging al the 
foot of the cliff, protects it from further assaults of the 
waves. But if the currents remove this material, the 
waves have fresh surface upon which to work. 

The bars at the mouths of rivers are nearly always the 
work of tidal currents, and so are many of the "banks" or 
shoals that obstruct straits and sounds. The North Sea 
contains many examples, and Lower New York Hay is 
full of them. 

Ocean currents undoubtedly transport an enormous 
amount of material. The Gulf Stream sweeps the shells of 
certain marine organisms from the Caribbean Sea as far 
north as the Carolina coast. The icebergs floated by 
arctic currents bring down a large amount of gravel and 
bowlders which are finally dropped in lower latitudes. It is 
by no means impossible that constant deposition of matter 
carried by ocean current's may have resulted in extensive 
changes of level in various parts of the earth's surface. 



QUESTIONS AND EXERCISES.— If possible, evaporate a small 
quantity of stream water of any kind in a beaker, or a porcelain dish, 
and note the result. Repeat the experiment with rain water. What 
inferences can be drawn that are applicable to the second paragraph 
of this chapter? 

Prove that ice, bulk for bulk, is lighter than water. 

If possible observe the effects of waves on the shore of any conven- 
ient body of water. Note the character of the work they do, or that 
you find they have done. Explain how waves make beach sand. 

If you are near the ocean, find the season of the year when the 
tides are highest. 

Refer to the map, p. 203, and note the direction of the tide waves in 
various parts of the Atlantic Ocean. What is their general direction 
in the South Pacific? 



WAVES, TIDES, AND CURRENTS 213 

Explain how ocean currents may affect navigation, either favor- 
ably or adversely. 

In one of the first chapters of his narrative, Robinson Crusoe speaks 
of the great indraught of the Gulf of Mexico ; what feature is meant? 

Of several thousand sealed and registered bottles thrown into the 
Gulf Stream, off the Florida Coast, a number were found afterward in 
the Caribbean Sea, along the West Indies; from the current chart, p. 
205, explain their movement. 

From any available cyclopedia, or other work of reference, prepare 
an account of one or more of the following: the Gulf Stream, the 
Maelstrom, the bore of the Amazon, the tides of the Bay of Fundy, 
the Hell Gate, or the effects of storm waves. ; 

COLLATERAL READING AND REFERENCE 

Pillsbury. — The Gulf Stream. United States Coast Survey. 

Mill. — Realm of Nature, pp. 154-184. 

Shaler. — Sea and Land, pp. 1-74, 187-222. 

U. S. Hydrographic Office. — Use of Oil in Storms. 



CHAPTER XII 
THE ATMOSPHERE AND ITS PROPERTIES: WINDS 

The atmosphere, or air, is the gaseous substance that 
forms the outer envelope of the earth. It rests on the 
land- and the water, and probably penetrates both to a 
considerable distance. Being a part of the earth, the 
atmosphere partakes of all the general motions of the lat- 
ter, but it has also certain movements of its own, which 
are very closely connected with life and its environment. 

The air is not a simple, or elementary substance; it 
is a mixture of several elements. The chief constituents, 
nitrogen and oxygen, have the proportion of about four 
parts of the former to one of the latter. Each of the 
remaining constituents, water vapor, carbon dioxide, and 
floating matter varies greatly in proportion. 

The newly discovered elements, argon, krypton, xenon, helium, and 
others form a very minute proportion of the atmosphere. 

The vapor of water rarely exceeds one part in one hundred 
of air. It is nevertheless a most important constituent, 
for it is in this form that the water is borne from the sea 
and shed upon the land. The floating particles of smoke, 
dust, and other matter are also essential, for they aid 
materially in condensing the water vapor. 

Physical Properties. — Air is highly elastic. Pressure 
decreases the volume, making the air denser. When the 
pressure is relieved, the air again expands and is rarefied. 

214 



THE ATMOSPHERE AND ITS PROPERTIES 215 



Air next the ground is denser than that above, because of 
the pressure or weight of the air overlaying it. The density 
decreases with the distance above the sea; at an altitude of 
two miles the density is only two-thirds that at sea-level. 

At a height of fifteen thousand feet the air is so rare that breathing 
is labored and the pulsations of the heart are very rapid. Climbing 
becomes difficult and any form of exertion is weary- 
ing. Water boils at about 85° (185° F.), a tempera- 
ture so low that it is difficult to cook vegetable&d)y 
boiling;. 



At sea-level a cubic foot of air weighs a 
little more than one Troy ounce. 

The force with which the air presses upon 
a given surface is called its tension; and, 
practically, the tension is a form of ex- 
pressing the pressure of the air. At sea- 
level, the pressure of about fifteen pounds 
on every square inch, or a little more than 
a ton on each square foot of surface. The 
tension varies slightly in different lati- 
tudes, being a little greater near the tropics 
than elsewhere. 

It is most convenient to measure the 
tension of the air by noting the height of a 
column of mercury, or quicksilver, that will 
just balance it. 

The instrument used for this purpose is 
called a barometer. It consists of a glass 
tube closed at one end, and filled with mercury. The 
tube is inverted, and the open end is placed in a small 
cup filled with mercury. The pressure of the air on the 
surface of the mercury in the cup sustains the column in 



J 



THE BAROMETER 



216 PHYSICAL GEOGRAPHY 

the tube. If the column in the tube rises it signifies that 
the pressure of air overhead is increasing; if it falls, the 
pressure is decreasing. 

At the level of the sea, the height of the barometer varies usually 
between 29.4 and 30.4 inches. Mercury is the most convenient substance 
to use for this purpose; it is a liquid metal that is heavy, and is not 
easily altered in physical properties. A water barometer would require 
a tube about forty feet in length; moreover, water freezes at 32° ]*'., 
while mercury remains liquid about seventy degrees lower. In the 
aneroid barometer, a vacuum box whose collapsible side moves a scries 
of levers, takes the place of the mercury. 

Effects of Temperature. — The atmosphere is warmed 
partly by the direct rays of the sun and partly by the heat 
radiated from the earth. It is also heated by compression 
and cooled by expansion. 

The intensity or degree of its heat is its temperature. The 
temperature of the air is measured by the expansion of a 
very fine column of mercury held in a glass tube— a ther- 
mometer. When a volume of air is compressed, it becomes 
greatly heated. Thus, air that descends from higher to 
lower levels, becomes heated because it moves into a le- 
gion where the pressure is greater. In the same wa}', a 
volume of rising air expands and is cooled, because it 
goes into a region where the tension is less. Heat expands 
the air; bulk for bulk, warm air is therefore lighter than 
cold air. If a volume of air is warmed from freezing 
temperature to that of intense summer heat its volume 
is increased nearly one-fifth. 

It is well to bear in mind that the common expression, "hot air rises 
because it is lighter," is not strictly correct. The hot air does not rise ; 
it is pushed upward and floated on the surface of the heavier cold air, 

The temperature of the air varies both with latitude 
and altitude. In equatorial latitudes the mean tern- 



THE ATMOSPHERE AND ITS PROPERTIES 217 

perature of the air over the sea is not far from 32° 
(90° F.); in polar regions it ranges much below 0° (32° F.). 
With respect to altitude the temperature falls at the 
rate of about one degree for every three hundred feet 
of ascent. The effect of altitude is very noticeable in the 
Andes. At the base of the mountains the heat is intense; 
at an altitude of ten thousand feet the air is mild; at seven- 
teen thousand feet, one is in a region of perpetual snow. 

Convectional Movements of the Atmosphere. — The 
air is everywhere in motion. The attraction of the sun 
and the moon undoubtedly causes atmospheric tides some- 
thing like the tides of the sea, but the effects are not well 
known. 

Sensible movements of the air are called winds. They 
are caused by changes either of temperature, or of pres- 
sure. When air is heated to a temperature higher than 
that surrounding, it expands and is pushed upward by the 
heavier air that flows in. Thus, at any locality where an 
updraught of warm air is taking place the pressure is re- 
duced, thereby forming an area of low barometer; on the 
contrary, if there is an accumulation of air at any locality 
the pressure is increased and there occurs an area of high 
barometer. When such inequalities of pressure exist, it is 
evident that winds will blow toward an area of low bar- 
ometer, and away from one of high barometer. Such 
movements of the air are everywhere taking place, and 
they are examples of the force of gravity. 

Equatorial and polar regions are not equally heated. 
The former receives the almost vertical rays of the sun; 
the latter only oblique rays. This results in two great 
movements, namely— a surface flow toward the equator, 
and upper currents from the equatorial toward polar regions. 



218 



PHYSICAL GEOGRAPHY 



But the colder air comes from the regions where the 
speed of the earth's rotation is comparatively slow, and 
enters latitudes where it is much greater; and not being 
able to acquire this speed at once it apparently lags behind, 
but practically produces a current to the westward. The 
rising air moves into a region in which the speed of rota- 
tion is not so great. It therefore moves to the eastward, 

as well as toward 
the polar regions. 
But in the two 
great movements 
d c s c r i b e d the 
easterly and the 
westerly compo- 
nents are much 
more noticeable 
than t h c polar 
and equatorial 
movements. The 
several areas in 
which the wind 
direction is fairly 
constant, consti- 
tute three great belts of winds — a belt of equatorial or 
easterly winds between two belts of westerly winds. These 
general movements are strongly marked on the oceans, 
but are greatly modified by the continents. In inland 
mountainous regions their direction might escape notice; 
in the great lowland plains they are more regular. 

The great convectional movements of the air result in belts of differ- 
ing pressure. In equatorial regions, the updraught of warm air creates 
a belt of pressure that is a little lower than the" normal. In the region 




GENERAL MOVEMENTS OF THE ATMOSPHERE 



THE ATMOSPHERE AND ITS PROPERTIES 219 

of the tropical calm belts, the downward movement of the air creates 
a belt of pressure a little greater than the normal. 

Trade Winds. — The surface winds which flow into trop- 
ical regions to take the place of the warm air that is 
"pushed upward, form the well-known Trade Winds. They 
therefore blow from the northeast and from the south- 




January. 



PREVAILING WINDS OF THE ATLANTIC 



July. 



east. Toward the centre of the belt they are practically 
steady easterly winds. 

The zone of Trade Winds is about fifty degrees in width. 
Its position is not stationary; it swings alternately north 
and south, as the seasons change. In the Atlantic Ocean 
the shifting of the belt is from eight to ten degrees; in the 
Pacific it is slightly greater. The belt reaches its northern 
limit in early autumn; its southern limit in early spring. 
The city of New Orleans is in the belt of Trade Winds in 
midsummer, and in that of the Prevailing Westerlies in 
winter. The Trade Winds are regular and constant the 



220 PHYSICAL GEOGRAPHY 

year round, their velocity being twelve or fifteen miles an 
hour. 

Formerly, when ocean commerce depended od sailing 
vessels, these winds were of great importance — hence their 
name. A vessel entering the Trade Wind belt could rely 
on steady winds with but little interruption. 

Along the line where the northerly and the southerly 
components of the Trade Winds meet, there is a narrow 
belt which is characterized by an absence of steady winds, 
but marked by almost constant rains. This belt is the 
updraught air and is called the Equatorial Calms, or 
Doldrums. It is scarcely more than two or three hundred 
miles in breadth. Sailing vessels are sometimes becalmed, 
requiring several weeks to cross it. 

Prevailing Westerlies. — The air that flows from equa- 
torial regions as an upper current, sinks to the surface 
in temperate latitudes, forming two belts of westerly 
winds, called Prevailing Westerlies. Like the Trade Winds 
both belts move northward and southward with the changes 
of the seasons. 

The height to which the updraught rises before it turns toward the 
pole is not known, except in two or three instances. On the Island of 
Hawaii, the Trade Winds reach an altitude of about twelve thousand 
feet. Above this elevation the winds have almost an opposite direct ion ; 
they are the winds that, a few degrees farther north, descend to become 
the Prevailing Westerlies. These winds are also called return-trades, 
anti-trades, and counter-trades. 

In the Northern Hemisphere the Prevailing Westerlies 
are neither so strong nor so steady as the Trade 1 Winds, 
and in higher latitudes they often give way to winds of 
northerly origin. On the coast of the Gulf of Mexico the 
Prevailing Westerlies, in the summer season, are reinforced 
by Trade Wind currents which are deflected by the high- 



THE ATMOSPHERE AND ITS PROPERTIES 221 

lands of Mexico. The resulting winds sweep up the 
Mississippi Valley and thence turn across the Atlantic, 
carrying with them the moisture that supplies the Eastern 
United States with rain. 

In the Southern Hemisphere, the Prevailing Westerlies 
are best known as the Roaring Forties. They cover a broad 
zone, and are an excellent illustration of the theoretical 
movement of the constant winds. When the trade route 
between Europe and the East Indies la$" around the Cape 
of Good Hope, the Roaring Forties were an important 
factor in commerce; the sailing master could depend on a 
twenty or thirty knot breeze the year round. It was then 
a common practice for vessels bound for Australia or New 
Zealand to continue eastward and return by way of Cape 
Horn. 

The descent to the surface of the upper currents which 
form the Prevailing Westerlies, is marked by calm belts — 
the Calms of Cancer, and the Calms of Capricorn. Like the 
zones of winds the calm belts also shift north and south 
with the season. They are interrupted by the continents 
and are scarcely noticeable within a hundred miles of their 
coasts. The Calms of Cancer are the well-known "Horse 
Latitudes." The Calm's of Capricorn are the more con- 
tinuous of the two calm belts. 

Many years ago, when most of the foreign carriage was made in 
sailing vessels, there was a brisk trade in horses from the ports of the 
New England States to the West Indies. Frequently the vessels were 
becalmed in the Calms of Cancer, and it became necessary to throw over- 
board half the number of horses, in order to save the remaining animals ; 
hence the name. 

Polar Winds. — The air that flows from equatorial regions 
toward the poles is deflected in an easterly direction, 



222 PHYSICAL GEOGRAPHY 

because of the earth's rotation. In theory, the polar winds 
should be a whirl 'of wind, from west to east. In the north 
circumpolar regions the theoretical whirl is noticeable to a 
limited extent; in south circumpolar regions it is marked. 

Monsoons. — Along coasts having a southerly or a 
southwesterly exposure, the summer winds have a direc- 
tion nearly opposite those of the winter season; that is, 
about half the year they blow from the sea; the remaining 
half toward the sea. These winds are called monsoons — a 
Malay word meaning "season." Two causes give these 
winds their character. 

In the first place, any great body of land is apt to be- 
come much warmer than the sea in summer and colder in 
winter. During summer there is an inflow of sea air. In 
winter the conditions are reversed; cold air flows from the 
and to the sea. In other instances, a region may be swe] >t 
by southeast Trade Winds at one part of the year, and by 
the northeast belt the remainder. The monsoons of the 
Mexican coast are probably due to this cause. 

The monsoon season does not keep pace with the ap- 
parent motion of the sun in its oscillation north and south. 
Like the "temperature season" it is about a month slow. 
The changes therefore occur in April and October instead 
of March and September, the dates of the equinoxes. 

The most remarkable monsoons, however, are those of 
the Indian coast. From April to October the southerly 
half of the belt of Trade Winds reaches far inland, pouring 
a deluge of rain upon the land. During the rest of the 
year the southerly part of the belt has moved southward, 
and the northerly half covers the coast, parching the land 
and withering vegetation. The tremendous updraught of 
warm air aids materially in giving strength to these winds. 



224 PHYSICAL GEOGRAPHY 

The " breaking" or change of the monsoon is usually at- 
tended by terrific storms. 

On account of its inland position, the central part of Asia is marked 
by great extremes of temperature. During summer its vast deserts are 
almost like a furnace, and the updraught of heated air is so enormous 
that it causes atmospheric disturbances two thousand miles away. 
In winter the dry air is chilled many degrees below that of the warm 
sea-air; being correspondingly heavier, it flows outward toward the 
ocean. 

The winds of the Gulf Coast and the lower Mississippi 
Valley may be regarded as monsoons, but they are neither 
so regular nor so strong as the Indian monsoons. 

Day and Night Breezes. — The difference between the 
temperature of day and night is sufficient to cause strong 
local winds. Thus, along the coasts, especially in warm 
regions, the updraught of the land causes a stiff on-shore 
wind during the day; at night, the air over the land, being 
more quickly chilled, flows down the slopes toward the sea. 
Coast fishermen frequently take advantage of such winds; 
they go out in early morning with an off-shore, and return 
at night with an on-shore breeze. 

Similarly, in mountainous countries the air upon the 
higher slopes is heated and cooled more rapidly than in the 
valleys. There often results a strong wind blowing up 
the valley 03^ day, and flowing downward at night. Moun- 
tain valley winds of this character are very common in 
almost every rugged country. 

A similar movement of air is noticeable in many large caves — es- 
pecially those that have openings at different levels. In the day time 
air in the cave may be colder than that outside, while at night it is 
warmer. At night a strong indraught of colder air at the lower entrance, 
and an updraught at the higher opening results. In the daytime these 
movements are reversed. 



THE ATMOSPHERE AND ITS PROPERTIES 225 

Local and Variable Winds. — Certain local winds are 
common in desert regions and arid lands, or else result from 
the proximity of the latter. Almost always they are dry 
winds. In general, they are either hot blasts blowing from 
a desert, or cold winds blowing into it. 

Thus, the Northers of Texas and Mexico are cold winter 
winds that blow from the highlands of the Plateau region. 
The Chinook and Santa Ana winds of the'western highlands 
of the United States are descending, and therefore warm 
winds. In southern Europe they are called Foehn winds. 

These names are applied to winds that have certain principles in 
common. Warm, moist air is pushed up the side of a mountain-range; 
being cooled, its moisture is condensed; the air then descending on the 
opposite, or possibly the same side, becomes warm very rapidly by its 
own compression. The effect is very marked ; snow disappears quickly 
— hence the popular name "snow-eaters." The descending air is not 
only warm, but it is so dry that in summer it withers vegetation. The 
Chinook wind gets its name from a locality in Oregon, but the name 
is now applied to warm winds that flow from the Rocky Mountains out 
on the plains to the east. Following a blizzard, it quickly melts the 
snow that covers the scanty feed of the cattle herds. The Santa Ana 
is a hot wind common in southern California and Mexico. These winds 
are now recognized as a factor in the wheat-growing region of the 
Saskatchewan and Athabasca valleys, in Canada. 

The Pamperos are similar winds flowing from the cold slopes of the 
Andes over the arid pampas of Argentina. The Punas of the Peruvian 
table-lands are of the same nature. 

In the vicinity of the African desert are the famous Mistral and the 
Etesian winds, both blowing from the snow-clad Alpine ranges toward 
the desert, while the Sirocco, like the Chinook, is a hot wind that in 
summer blows from the desert. The Harmattan is a warm winter 
wind, blowing from the desert to the Guinea coast. Aside from these 
there are several winds peculiar to desert regions. Chief among them 
is the Simoon, a fierce blast of hot air and rock waste, that neither man 
nor beast can face. It is common both in the Old World and the Ameri- 
can deserts. A milder form of this wind along the lower Nile valley is 
called the Khamsin. 



226 PHYSICAL GEOGRAPHY 

Desert Whirlwinds. — The most interesting deseri winds 
are the sand whirls, which occur when the air is still. Un< ler 
a hot sun the air next the earth becomes considerably 
heated, having a high temperature. Above the ground the 
air is cooler at the rate of one degree F. for every three 
hundred feet. Thus, a layer of heavy, cold air rests on a 
surface stratum that is much lighter. Such a condition 
cannot last long, and sooner or later a slight disturbance 
starts a column of air upward. 

Immediately the cold air begins to settle; as it descends, 
it forces the warm air upward through the self-made passage. 
The ascending column begins to whirl, and soon its motion 
is rapid enough to carry with it a cloud of fine rock waste. 

As a rule these whirls begin when the sun is two or 
three hours high, and continue until the wind begins to 
blow. The latter, by mixing the warm air with the cold, 
prevents their formation. Occasionally such whirls are 
vigorous "sand spouts." 

Physiographic Effects of Winds. — As an agent in 
wearing away the surface of the land, the wind acts in dif- 
ferent ways. It may alter the chemical composition of the 
rock with which it comes in contact. It may carry minute 
particles that cut away softer material. It may transport 
material from one place to another. The chemical action 
of air is due mainly to the water and carbon dioxide which 
it contains. It is manifested in the gradual crumbling of 
many granite and iron-bearing rocks, when the latter are 
exposed to the air. Dry air may affect locks by chemically 
withdrawing the moisture they contain; moist air may 
affect other kinds by chemically imparting water to them. 
In either case the rock may sooner or later crumble. 

The impact of minute particles carried by the wind is 



THE ATMOSPHERE AND ITS PROPERTIES 227 

noticeable in dry regions. Where sand storms are prevalent 
the surfaces of the hardest rocks are channelled, and 
polished from this cause. The "needles" or rock spires of 
such regions frequently are sculptured into fantastic forms 
by ceolian or wind-blown rock waste. 

Some years ago the author left an octagonal steel drill in an upright 
position exposed to the full sweep of a desert wind. Six months after- 




SAND-BEATEN ROCKS 

ward the angles of the drill had become almost obliterated by the 
impact of rock waste. The telegraph poles in the desert regions are 
frequently cut in two by the wind-blown rock waste. 

The transporting power of the wind is confined chiefly 
to sea shores and regions unprotected by vegetation. The 
wave-formed islands and barrier-beaches of the Atlantic 
and Gulf Coast have foundations of sea sediments, but 
the part above water consists of wind-blown material. 



228 PHYSICAL GEOGRAPHY 

The sand dunes of ocean and lake shores are excellent 
illustrations. In regions swept by monsoons the dunes 
travel seaward during one season and landward the other. 

A wave of sand about a mile long and seventy feet high at one time 
inundated a part of Cape Henlopen. A fire, which in 1828 burned off 
the woodland, started this dune on its travels. In 1845, General Joseph 
E. Johnston, then a United States Army engineer, noticed that north 
winds were picking up sand from the seaward face of the dune and 
carrying it over the crest to the landward side. Little by little the 
wave of sand overwhelmed a strip of pine barrens and filled a salt marsh 
beyond. Then it advanced upon a heavy growth of timber and, in 
time, covered all but the tallest trees, killing them as effectually as 
though they had been swept by fire. As the years passed by, the wave 
steadily advanced, and the wind began to uncover the buried surface 
in the rear. First the strip of pine barrens reappeared, and then the 
salt marsh was cleaned out and promptly reclaimed by the tide. Even 
the pine barrens began to show signs of life and a growth of young 
trees sprang up.- Still later, the advancing sand began to uncover the 
forest, and a border of dead trees now flanks the rear slope. Near the 
eastern end of the dune is Cape Henlopen lighthouse. A straggling 
ridge of the wave entered the yard, covered up the oil-house and the 
garden, and then took possession of the keeper's cottage. The Govern- 
ment acknowledged its inability to cope with the dune by erect ing a new 
cottage on the other side of the tower. 

Between the silt brought down by the Colorado River, 
and the fierce winds of that region, the Gfulf of California 
has been cut in twain, and most of the severed portion 
filled with rock waste to a height now considerably above 
sea-level; indeed, all through this region dunes are con- 
stantly forming, shifting, and re-forming. In western 
Nebraska, where the rainfall is not sufficient to grew pro- 
tective vegetation, dunes are common. 

On the Gascon coast of France, from the Gironde to the 
Adour, almost every stream has been blocked at its mouth 
by sand-drifts, and only the larger streams are powerful 
enough to force their way to the sea. In various parts 



THE ATMOSPHERE AND ITS PROPERTIES 229 

of the Mediterranean and the Baltic coast, the farmer is 
compelled yearly to shovel away tons of sand, and in the 
former locality an abandoned olive orchard half buried is 
no uncommon sight. 

Notable examples of the transporting power of wind 
occur in China. In the basin of the Hoang River deep 
seolian deposits cover many thousand square miles. 
These deposits, called loess — from a German word meaning 
"loose" — are thought to come fron# the desert region to 




DUNES OF SAND 

the westward. In many places the rivers have cut their 
channels through the loess, and the latter not only colors 
the water of the river, but imparts a yellow tint to the sea 
into which it flows. 

iEolian deposits have filled most of the valleys of the 
Basin Region of the western highlands. The ranges stand 
out in bold relief from an ocean of level, wind-blown rock 
waste. Many of the valleys of the Rocky Mountains have 
been filled and levelled in the same manner. Wind-blown 



230 PHYSICAL GEOGRAPHY 

drifts are very common in the northern part of the Missis- 
sippi Valley, where they are usually covered with growths 
of scrub oak. 

Various schemes for preventing the encroachment of dunes are 
employed. These are mainly of two kinds — barricades and vegetal inn. 
For the former the "sand fence," or movable panels much like the 
snow fence are employed. By far the most successful method, however, 
is the use of certain species of grasses. These are sown or planted 
when the sand is wet and their roots grow down far enough to reach sand 
that is always moist. Golden Gate Park, San Francisco, once an area 
of shifting dunes, has been reclaimed in this manner, and the plan has 
proved successful on Cape Cod, and the North Sea coast. 

QUESTIONS AND EXERCISES.— Devise or describe an experi- 
ment to show that air has weight; show that it is elastic; show 
that heating a volume of air causes it to expand; using a bicycle 
pump, show that compressing air warms it. 

What is the prevailing direction of the wind in the locality in which 
you live? Consult the records of the nearest weather station and 
compare the number of days of westerly winds with the number in 
which the wind is from other directions. 

The tropical calm belts are regions of descending air-currents; is 
the air apt to be chilled or warmed by this movement? 

Read Stedman's poem, " The Simoon," and compare it with the 
description in any standard cyclopedia. 

Why are northerly winds of the North Temperate Zone cold? 

Explain the manner in which street whirlwinds are formed. 

Note any instance of the physiographic effects of winds in the lo- 
cality with which you are best acquainted ; prepare a description of it. 

In what way do the general winds affect the temperature of the 
earth? 

Note any examples in which winds accomplish work that has an 
economic value. 

COLLATERAL READING AND REFERENCE 

TJ. S. Coast Survey. — Atlantic Coast Pilot Chart, for March and 
September, or February and August — any year. 

Le Conte. — Elements of Geology, pp. 1-8. 

Department of Agriculture. — Year Book for 1898, Band-binding 
grasses. 



CHAPTER XIII 

THE MOISTURE OF THE ATMOSPHERE, SEASONAL AND 
PERIODICAL DISTRIBUTION OF RAINFALL 



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The water vapor of the atmosphere, in a way, may be 
properly considered a part of it; but, if all the other con- 
stituents were absent, the water vapor would exist as an 
atmosphere in itself, and its move- 
ments would be the same practi- 
cally as those of the winds. But 
while the proportion of oxygen and 
nitrogen of the atmosphere do 
not perceptibly vary, that of water 
vapor is subject to rapid changes. 
The amount that is present at a 
given locality depends on one 
thing only — temperature. With a 
high temperature there may be a 
great deal of vapor mingled with 
the air; with a low temperature 
there can be but little. 

Changes in humidity are usually 
apparent to the sense of feeling, 
and one readily learns the differ- 
ence between moist and dry air. 
In many instances they may be 
forecast by observing the clouds. If the latter form rap- 
idly, or if small patches of cloud increase in size, the 

231 



THE HYGROMETER 



232 PHYSICAL GEOGRAPHY 

humidity is increasing. On the contrary, if the cloud area 
is becoming smaller, it is highly probable that the humidity 
is decreasing. 

Dew-Point. — At times it may be noticed that wet cloth- 
ing exposed all day to the air refuses to dry. The reason 
is that the air is already saturated, and because of this no 
further evaporation can take place. When all the vapor 
that can exist at a particular temperature is present, the 
air is said to be saturated or at the dew-point. This con- 
dition is unusual, however, except when rain is falling 
or during foggy weather; generally the amount present is 
considerably less than that required for saturation. From 
the amount present one may easily compute the relative 
humidity) thus, if half the quantity required to saturate 
the air is present, the relative humidity is fifty per cent. 
If the amount is near the dew-point, the air is moist; if 
the relative humidity is low, it is dry. Air that is moist 
at a given temperature may feel very dry at a higher tem- 
perature, even though no more moisture is present. The 
amount of moisture present in the air at any time is de- 
termined by an instrument called the hygrometer. 

Table VII., Appendix, shows the amount of water vapor there may 
be in the air at various temperatures. With the thermometer at 66° F., 
for instance, there may be seven'grains in each cubic foot of atmosphere. 
There might be less, but there can be no more; if more be added it 
would immediately condense — that is, change to rain or snow. From 
this table find whether or not there may be vapor in the air when the 
temperature is below freezing-point of water. 

Latent Heat of Evaporation. — Water may be changed 
to vapor by heat. When water boils it reaches the tem- 
perature at which it begins to change rapidly to steam. 
No matter how fierce the heat may be, the water (unless 



THE MOISTURE OF THE ATMOSPHERE 233 

it is confined) gets no hotter, and the steam given off has a 
temperature no higher than that of the boiling water. 

All this heat is absorbed in the work of changing the 
water to steam, and it is called the latent heat of steam. It 
has not been lost, however; it is merely stored-up energy. 
It is retained just so long as the water remains in the form 
of vapor; it is given out the moment the vapor is con- 
densed, or changes to a liquid. 

This property of water is one of the greatest importance, 
for, as will be shown, it is a chief factor in the atmospheric 
disturbances called storms. The energy of the heat thus 
rendered latent is very great. For every pound of water 
converted to steam, about as much heat is required as would 
raise half a ton of water one degree F. 

Dew. — Dew is the moisture that gathers on the ground, 
or on exposed objects, after sundown. Both the air and 
the ground lose a part of their heat. But the latter cools 
more rapidly, and the layer of air next the ground is chilled 
below the dew-point. When this occurs, the excess of vapor 
in the form of minute drops gathers on the grass and on 
other objects near the ground. The moisture that gathers 
on the outside of a glass of iced water is an example. 

Dew does not always form at night, and for this there 
are several reasons. A stiff breeze may keep the air 
thoroughly mixed, and thereby prevent any part of it 
from being chilled to the dew-point. The air may contain 
so little vapor that a fall of fifteen or twenty degrees does 
not bring the temperature to the dew-point. A cloudy 
sky, especially if the clouds hang low, prevents the radia- 
tion of heat, and the formation of dew. 

Sometimes dew forms copiously with but a slight fall of temperature, 
while perhaps on a following night, none may appear, though the tern- 



234 PHYSICAL GEOGRAPHY 

perature is much lower. An inspection of the table on p. 380, will 
explain how this may occur. If there were seven grains of water 
vapor in each cubic foot of air, a fall of temperature from 68° (F.) to 64° 
would be attended with dew; but if only three grains were present, the 
thermometer might sink as low as 40° without any sign of dew. A 
cloth screen within four or five feet of the ground will sometimes have 
the same effect as low clouds in preventing the gathering of dew. 

The amount of moisture in the air varies much, both in 
time and place. In tropical regions, and those near the 
sea, the amount is usually great. Sometimes it is so near 
the point of saturation that the air becomes hazy. In 
such regions dew forms copiously. In temperate latitudes 
the amount is much less than in tropical regions. 

In the lowlands of the Pacific coast, where there are no 
summer rains, the fall of dew in early summer is excessive. 
The same phenomenon occurs in most mountain valleys. 

If the temperature of the surface be lower than 0° 
(32° F.), the moisture may pass immediately into the crys- 
talline form, hoar frost, or white frost. Sometimes the 
minute frost crystals form in the air, but usually they 
accumulate on the grass, the leaves, and other objects near 
the ground. Sometimes the frost is simply frozen dew; 
and if it takes the form of a thin varnish of ice that i\"<'* 
not appear crystalline, it is called black frost. The latter 
term is also applied to the peculiar appearance of plants 
whose juices are frozen. 

Except at considerable altitudes frost does not occur 
in tropical regions. In temperate latitudes it may occur 
at any time between late fall and spring. Late spring 
frosts are apt to occur after fruit-trees have budded, and 
they are therefore commonly known as hilling frosts. The 
cold wave that follows a spring storm is very apt to lower 
the temperature to the freezing-point, and if the air be 



THE MOISTURE OF THE ATMOSPHERE 235 



moist, a killing frost commonly occurs. Fortunately its 
occurrence usually can be predicted with, a considerable 
degree of certainty. 

Clouds. — When the temperature falls so low that a part 
of the vapor is condensed, the latter does not at first 
gather into large drops; on the contrary, the drops are so 
minute that they float in the air. f This floating mist of 
the air is called fog if at the ground, or cloud if it forms 
higher in the air. 

Nearly always the air is filled with dust motes and other 
floating matter, and much of the condensing vapor gathers 
on these. Not only do the dust motes form a lodgment 
for the condensing vapor, but they cool more rapidly than 
the air, and thereby quicken 
the process of condensation. 
The floating matter in the 
air thus becomes an active 
agent in cloud formation. 

The cooling of the air be- 
low the dew-point is the 
essential feature, and this 
may occur in several ways. 
Thus when a mass of air, is 

pushed upward, not only is it chilled by going into a cooler 
position, but it is also cooled by its own expansion. It is 
probable that the greater amount of cloud is formed in this 
manner. Thus, in equatorial regions, where the updraught of 
warm, moist air is constant, there is a perpetual cloud-belt. 

The intrusion of warm, moist winds into cold regions, or 
vice versa, is also a common cause of fog and cloud. The 
fogs and cloud banks so common off the coast of Newfound- 
land are formed in this way. 




CIRRO-STRATUS CLOUDS 



236 



PHYSICAL GEOGRAPHY 



Whenever a warm sea-wind blows against a high moun- 
tain slope, a part of the air is driven up the slope, and, 
some of its moisture being condensed, cloud is formed. 
Almost always high mountain crests near the ocean are 
shrouded in clouds, and not infrequently a cloud banner 
streams from the leeward side of a high peak. 

Cloud banners were noticed in the Alps by Professor Tyndall, and were 
first described by him. They may be often seen streaming from the 
summit of Mount Tacoma and of Mount Hood. 

Cloud Nomenclature. — Clouds usually take charac- 
teristic forms, and these are governed mainly by the 

presence or absence of wind, 





MACKEREL SKY 



and also by their height. 
Cirrus clouds arc light and 
feathery in appearance and 
commonly white in color. 
These clouds take various 
forms. When they are flaky 
or fleec}' they are the 
"mackerel" clouds heralded 
by sailors as forecasters of 
fine weather; but cirrus "streamers" are frequently found 
as advance indication of an approaching cyclone. 

This indication has had a recognized place in weather-lore for two 
thousand years. It is mentioned in Virgil: 

Tenuia . . . lame per ccelum vallera fcrri, 

and it is found among Teutonic peoples, as well; hence the popular 
saying: 

Mackerel sky, twelve hours dry. 

Often the patches of cirrus cloud are ranged in parallel 
strips; and occasionally they radiate like the spokes of a 
wheel. Commonly their altitude is between five and ten 



THE MOISTURE OF THE ATMOSPHERE 237 

miles. On account of their great height it is obvious that 
they consist of minute ice crystals. Cirri may form above 
another cloud, the two being apparently related, but they 
never form under other clouds. 

Cumulus clouds are the day clouds of summer weather. 
They appear like great, rounded domes resting on a hor- 
izontal base. A gently warmed current of air rises until, 
being chilled both by expansion and altitude, condensa- 




CUMULUS CLOUDS 



tion begins. The process continues until a dense mass 
of cloud is formed. This form is the almost universal 
cloud of tropical regions. It is abundant in warm tem- 
perate climates, but rare in cold latitudes. It does not 
form at night nor in cold weather, for the simple reason 
that the updraught of warm air is too feeble, and there is 
not enough vapor present to form clouds of sensible dimen- 
sions. Cumulus clouds have no especial significance as 
weather forecasters. They indicate nothing more than 



238 



PHYSICAL GEOGRAPHY 



the presence of moisture and, las a rule, their Bize shows 
whether there is considerable vapor or only ;t little. If, 

however, any cloud mass loses its flat base, becoming 
ragged or festooned at the lower side, high winds and local 
showers may be expected. 

Stratus clouds are so called because they arc Hal layers 
of nearly uniform thickness. Usually they arc wry low, 
and contain a great amount of foreign mailer. They arc 
commonly observed at morning and evening, and stillness 

of air is essential to their 

formation. 

Not infrequently a column of 

smoke, from a factory chimney or 
a steamer's smoke-stack, becomes 
the nucleus of a stratus cloud. 
The smoke ascends until buoy- 
ancy and gravity balance each 
other, and it then settles in the 
form of a thin, flat layer. Bach 
particle becomes a surface of con- 
densation, and the cloud matter continues to gather until it is swept 
away by the wind, or the conditions of temperature are changed. 

The Nimbus is the shapeless rain-cloud. The upper part. 
consists of light fog or mist; the lower, of falling drops. 
Usually it seems to form in clear air, and it gathers when 
the temperature reaches the dew-point. 

All clouds are moved hither and thither by the wind, 
but (lie matter composing the cloud itself is usually in 
motion even when the cloud is still. A study of a summer 
cloud shows that it. is constantly moving within itself, 
('loud may he considered as floating "water dust," but in real- 
ity the minute drops are always slowly falling. The droplet 
falls until it reaches a region of greater warmth; then it is 




STRATI'S CLOUDS 



THE MOISTURE OF THE ATMOSPHERE 239 

changed to vapor, and the latter at once ascends until it is 
again condensed — the process being constantly repeated. 

Rain. — The difference between rain and cloud consists 
very largely in the size of drops, but there is also a differ- 
ence in their physical condition. The drops of cloud 
matter are minute, and practically they float in the air; 
those of rain are each many thousand times as large, and 
fall quickly to the ground. The (^uscs that operate to 
produce fog and cloud, however, also produce rain — 
namely, the cooling of water vapor below the dew-point. 

The vapor precipitated as rain may pass through the 
cloud stage, it is true; but the latter is one of short dura- 
tion, and, as a rule, when condensation begins, it proceeds 
rapidly. Rain is rarely associated with fair-weather 
clouds and, excepting local showers, it is not derived from 
them. In general, rains arc derived from warm ocean 
winds that, blowing inland, are chilled. 

More rain falls in tropical regions than elsewhere; the 
equatorial cloud-ring is also a rain-belt, and under it pre- 
cipitation is almost continuous. The amount of rain fall- 
ing in the torrid zone is sufficient to cover it to a depth 
probably of more than one hundred inches. In the tem- 
perate zone it is a little more than one-third, and in polar 
regions about one-eighth as much. 

Rainfall is not uniform for all places in the same lati- 
tude. On slopes that face ocean winds it is greatest, 
while in regions shut off from the sea by high ranges it is 
little or nothing. For example, on the southern slope of 
the Himalayas the precipitation varies from two hundred 
to six hundred inches; on the north side it is less than 
ten. On the western slope of the Sierra Nevjida and Cascade 
Ranges it is ten times as great as on the eastern. 



THE MOISTURE OF THE ATMOSPHERE 241 

The heaviest annual fall is probably at Cherrapunji, India, where 
the average is about 500 inches. In August, 1841, the total fall for the 
month was 264 inches, and in 1861 the yearly fall reached the enormous 
amount of 905 inches — about 2.5 inches a day. On June 14, 1876, 
40.6 inches fell in twenty-four hours. In the three days ending February, 
1893, an aggregate of 35.8 inches fell at Brisbane, Australia. In the 
United States 21.4 inches fell at Alexandria, Louisiana, in one day, 
and at Triadelphia, West Virginia, 6.9 inches fell in fifty-five minutes. 
All these instances, however, are very unusual. Commonly, not more 
than two inches fall in a day. 

As a rule, precipitation is greatest 'In the vicinity of the 
coast and decreases toward the interior. If a mountain 
range faces the coast, however, it may be heavier on the 
slope facing the sea than along the immediate coast. 

On the Atlantic coast of the United States the rainfall is 
forty inches or more; west of the one hundredth meridian 
it is less than fifteen. On the northern shores of South 
America it is over one hundred inches; a few hundred miles 
inland it is about one-quarter as much. In the uplands 
of the eastern slope of the Andes it again increases. 

The greater the distance from the coast the more abnormal also is 
the character of the rainfall. In the Basin Region of the western 
United States, the rain is restricted to showers of short duration, and 
these often take the form of cloud-bursts. There is a sudden darkening 
of the sky, a terrific downpour of water — perhaps three or four inches 
in fifteen minutes — and then the sun is again licking up the water from 
the almost hissing rock waste. 

Periodical Rains. — Not only does the amount of rainfall 
vary in different localities, for the reasons noted, but there 
is also much difference in the time of its distribution. In 
some localities it comes in the form of occasional showers; 
in others long periods of rain and drought alternate at given 
intervals — that is, the rainfall is periodical and seasonal. 

A study of the wind chart, p. 240, will help to explain 
the periodical character of rain in certain localities. The 



242 PHYSICAL GEOGRAPHY 

slopes of the continents that face ocean winds, as a rule, 
have periodical rains. Thus, most of the western coast 
of North America faces the Prevailing Westerlies of the 
Pacific Ocean. In summer these winds are blowing into a 
region that is warmer, and therefore but little rain falls. 
In winter, on the other hand, the temperature of the land is 
much lower, and therefore rain may be of daily occurrence. 
On the Mexican coast, where the climate is almost always 
mild, but little rain falls. Along the coast of the United 
States it varies from ten or twelve inches at San Diego to 
sixty or seventy at Puget Sound; at Sitka, Alaska, it is 
about one hundred inches. How will the difference in 
latitude explain this? On the Atlantic coast of Europe 
the conditions are much the same; most of the precipita- 
tion occurs during the winter months, but on account of 
high latitude a considerable rain falls in summer. 

In regions visited by periodical rains, not infrequently the air is so 
loaded with dust, at the end of the dry season, that the first rain is 
discolored and even muddy. The yellow and golden rain, once a great 
mystery, is commonly due to the pollen of pine. Examined under a 
microscope the character of this pollen is such as to leave no doubt as 
to its origin. Showers of frogs, fishes, and angleworms have been 
reported, but not an instance has been substantiated. It is not im- 
possible that a water-spout might whirl a school of fishes into the air, 
and then over the land, but no tornado known has been so selective as 
to confine itself exclusively to frogs and angleworms. The latter simply 
emerge from their hiding-places at the onset of the shower. 

Among other abnormal showers are the rains from cloudless skies. 
Instances are common, especially in mountainous localities. The pre- 
cipitation in such cases is very slight and the showers rarely cover 
more than a few square miles. The sky is cloudless merely because 
there are not enough drops in the air at any moment noticeably to in- 
terrupt the light. 

In tropical regions, where the winds have an easterly 
origin, the easterly slopes receive the heaviest fall of rain. 



THE MOISTURE OF THE ATMOSPHERE 243 

In these regions, however, the rain follows the passage 
of the equatorial cloud-belt back and forth. This belt 
is comparative^ narrow — scarcely five hundred miles in 
breadth. During the spring months of the Northern Hemi- 
sphere it moves northward with the sun, deluging the 
land over which it passes with almost continuous rain. 
After reaching its northern limit it turns southward, re- 
passing over the same belt. In the American continent 
the cloud-belt does not pass far south of the equator; in 
Africa it reaches much farther south. 

At each tropic, the limit of the cloud-belt, there will be 
one rainy and one dry season, while at intervening latitudes 
there may be two. Which of these conditions applies to 
Cuba ? — to the Caribbean coast of South America ? 

Regions swept by monsoons usually have seasonal 
rains. During one part of the year the winds blow from 
the land; the remaining time from the sea. The rains of 
the Indian coast of Asia are an excellent example. During 
the winter months the prevailing winds are land winds; 
but with the bursting of the April monsoon the season of 
heavy rain begins. 

Storm Rains. — A large part of the land surface of the 
earth is watered, not by seasonal and periodical rains, but 
by the rain that comes with the movements of the atmos- 
phere known as storms. These regions as a rule are either 
far inland, or else high mountain ranges shut them off from 
the reach of ocean winds. 

That part of the United States east of the Rocky 
Mountains is an example. The great highland ranges 
precipitate the moisture brought from the Pacific, and 
there are no seasonal rains. Moisture gathers from the 
Gulf and the ocean, but for the greater part it is not con- 



244 PHYSICAL GEOGRAPHY 

clensed until the whirling movement of the air which con- 
stitutes the storm, takes place. These storms occur so 
frequently that almost every part of the region receives a 
plentiful supply of moisture. 

Effects of Altitude. — As a rule, more rain falls at sea- 
level than at higher altitudes; very little falls above the 
height of ten or twelve thousand feet. On mountain 
slopes, however, the greatest precipitation takes place be- 
low three thousand and five thousand feet. The reason is 
twofold. In moderately warm regions rain clouds com- 
monly do not reach much above this altitude; moreover 
at this height the ground may be cold enough to condense 
moisture when it is too warm to do so at a lower level. 
This fact is often observed in desert regions. 

Rainless Regions. — There are two principal causes 
for the existence of rainless regions. There may be a 
barrier of high mountains that shut off rain-bearing winds; 
or, vapor may pass into a warmer region where it cannot 
be condensed. The Basin Region of the western high- 
lands, the basin north of the Himalaya Mountains, and the 
Andine desert, are examples showing the effects of moun- 
tain barriers. The mountains reach higher than the rain 
winds. The two African deserts and much of the Mexican 
coast show the effects of hot inland regions. The ocean 
winds that penetrate these regions are warmed and not 
cooled, and therefore the air becomes relatively drier. 

Snow. — When the condensing vapor freezes before it 
can gather into drops, snoiv results. It is evident, more- 
over, that snow cannot form unless the temperature of the 
air is as low as 0° (32° F.). If condensation takes place 
very slowly in still air, the moisture aggregates into beau- 
tiful crystalline forms, but if condensation is rapid or if 



THE MOISTURE OF THE ATMOSPHERE 245 

there is wind, the flakes consist of tangled masses of 
broken crystals. 

With one or two exceptions all the illustrations of snow crystals are 
copies of drawings made in the arctic regions by Captain Scoresby. A 
few drawings have been made by Professor Tyndall, and recently ex- 
cellent photographs have been obtained; these show that ice crystals 
and snowflakes are not so regular as those observed by Scoresby. In 
order to obtain good specimens of crystals, they must be gathered on a 
perfectly still day when the temperature is several degrees below the 
freezing-point. It is best to catch them on ?.. piece of black cloth, and 
if they are to be examined under a microscope the glass slide on which 
the flake rests should be covered with the same material. The crystal- 
line forms observed in sunshine are materially different from those 
found in cloudy weather. 

Inasmuch as snow depends on a low temperature, it is 
evident that its distribution is governed both by latitude 
and altitude. In polar regions snow covers the ground 
the greater part of the 3 r ear, and at a little distance from 
the sea it never melts. In equatorial regions the line of 
perpetual snow is about sixteen thousand feet above sea- 
level; in temperate latitudes it varies from seven thousand 
to twelve thousand feet. 

Hail. — Hail consists of pellets of ice, formed in the air, 
and a shower of them constitutes a hail storm. Usually a 
hailstone consists of alternate shells of snow and crystal- 
line ice. In some instances sharp, dog-toothed crystals 
of ice project from the outer surface. Hailstones vary 
in size from tiny pellets to masses an inch in diameter. 
Larger stones occur, but usually they are formed by the 
cohesion of small ones. 

Hail storms are more frequent in warm weather than in 
cold. For reasons unknown certain localities are especially 
subject to them. They frequently accompany thunder- 
storms, and the formation of the ice pellets results from 



246 PHYSICAL GEOGRAPHY 

whirling updraughts that carry the rain drops far upward 
into air of freezing temperature. As a rule, hail storms 
are of only a few minutes' duration, and the amount falling 
is a small fraction of an inch in depth. 

In 1S88, at Moradabad, India, bail fell to a depth of several inches, 
and in one district two hundred and thirty-five people were killed. In 
June, 1879, a storm swept over central New York and Massachusetts, 
during which stones seven inches in circumference fell. In July. 1880, 
a hail storm destroyed the crops in the vicinity of Waupaca, Wisconsin. 
The shower covered an area of forty square miles. Stones from six 
to ten inches in circumference fell. In July, 1881, the fall of hail at 
Cumberland, Maine, was so great that drifts two feet deep were observed 
twelve hours afterward. In June, 18S2, at Dubuque, Iowa, stones 
weighing twenty-eight ounces were found. In August, 1883, at Gray, 
Iowa, the drifting hail covered the fence tops. In June, 1886, so much 
hail fell in Grand Forks County, Dakota, that it did not all melt for 
thirty hours. In a single storm that passed over a small area in Dakota, 
a quarter of a million acres of wheat were destroyed. 

QUESTIONS AND EXERCISES. — Observe the temperature and 
find the greatest amount of moisture there may be in the atmosphere 
at the time of recitation. Find the annual rainfall of the neighbor- 
hood in which you live by striking an average of the yearly precipita- 
tion for at- least ten years. ( The statistics may be learned from the 
nearest Weather Station.) 

Fill a brightly-polished tin cup, or a nickel-plated shaker half full 
of water; add finely -broken ice and stir until a mist appears on the 
outside of the cup. Ascertain the temperature of the water; this is 
approximately the dew-point. 

Make a record of the early and late frosts for the year. What fruit 
crops are injured by killing frosts in the neighborhood in which you 
live? 

Learn, from the nearest Weather Station, the months in which the 
greatest amount of rain or snow falls; — the least. 

What crops or plants of commercial value would suffer or perish 
if the rainfall in the State in which you live were decreased one- 
third? 

Note the character and kinds of cloud visible during several days; 
at what time were stratus clouds visible? 



THE MOISTURE OF THE ATMOSPHERE 247 

Explain how smoke may gradually gather cloud matter. Why is 
this most apt to take place toward evening? 

The receiver of a rain gauge is a cylindrical cup four inches in 
diameter. For convenience of measurement the water caught is 
poured into a glass tube one inch in diameter : a depth of one inch of 
rain in the receiver will make how many inches in the tube? 

Explain how a crust forms on the surface of snow. 

At a convenient opportunity, catch flakes of snow on a piece of 
black cloth ; examine them with a magnifying-glass and make draw- 
ings of their shape. {Observe the conditions noted on p. 245.) 

• 
COLLATERAL READING AND REFERENCE 

Tyndall. — Forms of Water. 

XJ. S. Weather Bureau. — Monthly Weather Review. Midsummer 
and midwinter issues of any year. 

Greely. — American Weather — pp. 77-81, 134-162. 
Waldo. — Elementary Meteorology — pp. 142-165. 



CHAPTER XIV 



THE MOISTURE OF THE ATMOSPHERE. 
STORMS 



CYCLONIC 



Both on the land and at sea there are regions of con- 
siderable area that normally are not swept by regular and 
constant winds. On the sea these are the calm belts; on 
the land they are regions from which the winds are shut 
off by mountain-ranges, or disturbed b}^ broad stretches 
of land. On the sea the shifting of the calm belts with the 
season brings various parts successively under the influ- 
ence of the regular winds. 
On land the regular winds 
usually exist as upper cur- 
rents, while at the surface 
the winds are local and vari- 
able; the upper currents, 
moreover, are so high that 
they are too cold to contain 
much moisture. 

SucK regions do not re- 
ceive seasonal rains. The 
land areas, in some instances, receive none at all, except from 
an occasional cloud-burst; but in many cases a consider- 
able rainfall results from the movements of local winds. 
That part of the United States east of the Rocky Moun- 
tains is an excellent illustration. It receives no moisture 
directly from the constant winds; yet about every part of 
it east of the 2,000-foot contour is so generously supplied 

248 




STRATUS CLOUDS DISTURBED BY 
AN UPDRAUGHT 



CYCLONIC STORMS 



249 



with rain that it is one of the most productive regions 
of the world. 

Whenever a local wind occurs, one of two conditions is 
pretty apt to exist. Either there is an updraught toward 
which the wind is blowing, or else there is a great accumu- 
lation of air from which the air is spreading outward. 
These local disturbances 



50 


N. HEMISPHERE 


50 


/^iC~^\ 


40 


rWy^J 


40 


30 


/7^r~*^ 


30 


20 


^fev, 


20 


10 

10 


VJ o&B« ? 


10 

10 


EQUATORIAL CALMS 


-<£0& rL 


20 


r^f^ 


20 


30 


"A^w^Z" 


30 


40 


\^y~^) 


40 


50 


^-"v^^/ 


50 


S. HEMISPHERE 



constitute the condi- 
tions popularly known 
as storms. Moreover, in 
either case the move- 
ment of the air sooner 
or later develops into a 
whirl. The wind that 
blows toward an up- 
draught or a depression 
forms a cyclone; that 
which blows outward 
from a high bank of air, 
an anticyclone. These 
disturbances originate 
both on the land and at 
sea. They are usually 
indicated by a changing 
barometer; hence a cyclone is often described as an area 
of low barometer — or simply a "Low" — and the anticy- 
clone, one of high barometer. As a rule, both the cyclone 
and the anticyclone are local disturbances, and therefore 
they are carried along by the great currents of the air, just 
as an eddy formed in a river is carried along in its flood. 

Cyclonic movements therefore travel westwardly in low 
latitudes and eastwardly in latitudes beyond the tropics, 



NORMAL CYCLONE TRACKS 



250 



PHYSICAL GEOGRAPHY 



because these are the prevailing directions of the winds. 
Therefore, when a cyclone has formed, the track which it is 
likely to follow can be predicted with considerable accuracy. 
The direction of the whirl is also certain; in the Northern 
Hemisphere it is opposite that of the clock hands; in the 
Southern Hemisphere, with the clock hands. A knowledge 
of these facts enables the mariner not only to avoid a cy- 
clone, but also to steer out of it whenever he may be over- 
taken by one. 

In the tropics the cloud-ring rarely exceeds five hundred miles in 
diameter, and the circle of dangerous winds is scarcely more than half 
as great. In higher latitudes, however, the diameter of the storm in- 
creases. The wind is more violent in tropical than in higher latitudes. 

The direction of the whirl probably results from the conflict of winds 
as they approach the updraught. Of all the currents setting toward 
the storm centre, the northeast Trade Wind is the strongest. As it 
approaches the storm centre it is opposed by weaker winds from the 
north, northwest, and west. The Trade Wind is bent therefore toward 
the east and forced to rotate in the manner described. 



Tropical Cyclones. — Tropical cyclones usually origi- 
nate within a few degrees of 
the equator. They are the 
hurricanes of the West In- 
dies and the typhoons of the 
China Sea. The storm area 
extends over a surface vary- 
ing from a few hundred to 
more than a thousand miles 
in diameter. The illustra- 
tion, p. 249, shows roughly 
the track which, ordinarily, one of them follows. What is 
its direction in tropical latitudes? in latitudes beyond the 
tropics? 




'STREAMERS" OF CIRRUS CLOUDS 
—THE FORECAST OF A CYCLONE 



CYCLONIC STORMS 251 

The real beginning of the tropical cyclone is the dead 
calm that for a few days precedes it, for a quiet atmosphere 
is a necessary condition to its formation. The first es- 
sential condition is the overheating of the air next the 
water — precisely the same condition that formed the be- 
ginning of the desert whirl (p. 226). But while the stratum 
of air that causes the desert whirl is only a few hundred 
feet in height and of very small area, the atmosphere dis- 
turbed by the tropical cyclone is, perhaps, several thousand 
feet high and many thousand miles in extent. 

The longer the sun beats upon the glassy surface of 
the water, heating the air nearest to it, the greater will be 
the energy of the storm when it begins. Moreover, there 
is one element present in the tropical cyclone that is not 
found in the case of the desert whirl — namely, the vapor 
of water. This is the most important distinction between 
the two. Finally, an updraught of air occurs where the 
resistance is least. The moment this occurs, the rising air 
already near the dew-point is chilled by its own expansion, 
and a part of its moisture is precipitated. The fall of rain 
sets free an enormous amount of latent heat, and a furious 
updraught at once takes place. 

The latent heat of the moisture set free gives to the 
cyclone its great energy. This is its fuel, and so long 
as the supply lasts, just so long will the cyclone con- 
tinue. The ascending air at first is moist and warm; but 
after its moisture has been condensed, the heat set free 
renders it warmer, thereby increasing the updraught. 

The nearer the centre of the cyclone, the stronger is the 
wind. The "eye" of the storm, or the centre of the 
whirl, is the updraught of the cyclone, and here brief in- 
tervals of sunshine alternate with torrents of rain. In the 



252 PHYSICAL GEOGRAPHY 

centre of the storm the barometer stands lowest — perhaps 
two inches lower than it is beyond the edge of the storm. 

The barometer gives first warning of the approach of the cyclone. 
During the few days preceding, the barometer is perhaps above its 
normal height and the weather pleasant and clear. Sooner or later tin- 

barometer begins to show signs of unsteadiness, and at the same li 

a long, low, ocean swell becomes perceptible. Possibly a streamer or 
two of cat-tail clouds pointing toward the zenith is seen in the south or 
southwest, and a whitish arc near or on the horizon indicates the bearing 
of the centre. In a short time the barometer begins to fall — slowly 
at first, and then more rapidly. A halo gathers around the sun; the 
ocean swell increases, the sky grows purple, and fitful puffs of wind come 
from the north. There can no longer be any doubt of the approaching 
storm, and the prudent master has already made everything snug and 
ready for the coming blow. Soon a heavy bank of cloud looms up 
from the horizon. This is the cloud- ring that marks the edge of the 
storm, and the circle of dangerous winds is not far away. Finally the 
wind, already very squally, bursts into a gale, and veers to the north- 
ward, and soon the storm is in full force. If, by any means, the course 
of the ship has not been altered, or if, through accident, it is carried 
with the wind, the latter will increase to hurricane strength, and not even 
the smallest storm-sail will stand against it. Then almost in a twinkling, 
the wind lulls and the ship is in the eye of the storm. The sky alter- 
nates between inky blackness, with terrific down-pours of rain, and 
moments of misty, yellow light. Perhaps half an hour passes, and the 
opposite side of the cyclone strikes the vessel. At that moment the 
wind again bursts upon the ship from the opposite direction. Nothing 
but a stanch vessel can ride through such a storm. A square-rigged 
ship is apt to have her yards stripped off, even if the masts are not 
snapped. 

The cyclone may be considered as an edd}^ in the great 
tropical easterly current of the air along with which it 
moves. When the whirl lias reached the belt of Prevailing 
Westerlies, it is carried along with that current also. 
Knowing the direction of the whirl and the path of the 
storm, it is not difficult to lay the course of the vessel 
out of the way of the cyclone. For this purpose "storm 



CYCLONIC STORMS 



253 



cards," or diagrams similar to that below, are conven- 
ient. The distance of the storm centre can be estimated 
only to a rough degree, but the bearings can be obtained 
with a high degree of probability. Facing the wind the 
storm centre is on the ob- 
server's right hand. 

The accompanying storm 
cards are adapted for use in any 
cyclones of the northern hemi- 
sphere; the upper diagram is 
available for the route between 
New York and English ports. 
The small arrows fly with the 
wind; the long arrow represents 
the storm track through the belt 
of latitude to which the diagram 
applies. For West Indian hurri- 
canes the storm track recurves 
as follows: June and October, 
latitude 20° to 23°; July and 
September, latitude 27° to 29°; 
August, latitude 30° to 33°. 
When a falling barometer and 
other signs indicate the approach 
of a cyclone, select the diagram 
that applies to the latitude and 
plot the position of the ship ac- 
cording to the direction of the 
wind. In low latitudes, for in- 
stance, the wind is N NE; the vessel is then in the position that is 
shown on the lower diagram, and is in the dangerous semicircle. If 
possible it is best to lie-to (on the starboard tack), and observe the 
wind, (a) If it freshens without shifting, the vessel is certainly in 
the storm track. In this case the navigator keeps off, with the 
wind on the starboard quarter, holding to the course, (b) If it shifts 
to the right, the ship is to the right of the storm track and should 
be put on the starboard tack, making as much headway as possible 
until obliged to lie-to. (c) // it shifts to the left, the ship is on the left 
of the storm track and should be brought about until the wind is on the 




%■%■ 

l //SW. °ANGEfl , 

HE/ENE. E. "S 

% *r0 % % 

y<ii sw. ys sw. 
STORM CARDS 



254 PHYSICAL GEOGRAPHY 

starboard quarter, lying-to on the port tack if necessary. In scudding, 
the wind should be kept always on the starboard tack to run out of the 
storm. If the vessel is in the latitude where the cyclone probably 
recurves (according to the month) the middle diagram is applicable. 
Suppose that the wind is S E; the vessel then has the position marked 
in the middle diagram. It is on the right of the storm track and should 
run out as in (6), previously noted. In high latitudes the upper diagram 
is indicated. Suppose that the wind is N E. The ship then has the 
position shown to the left of the storm track, in the navigable semicircle, 
and should be brought about as in (c), previously noted. 

Winter Cyclones. — Some of the fiercest storms of the 
higher latitudes, however, do not originate anywhere within 
tropical regions. These are the extra- tropical or winter 
cyclones, and the fierce winter storms of the North Atlan- 
tic Ocean are examples. These storms do not originate in 
a dead calm, because there is no long-continued calm 
weather where they form; and it is apparent that the}- are 
not formed by the overheating of the air next the surface 
of the water. 

It is thought that they result from the intrusion of 
cold, north winds into the region of warm and moist air. 
to the southward. In any case the condensation of moisture 
creates an updraught that quickly develops into a whirl. 
But if, at the time of intrusion, the cold air takes the 
upper position, the equilibrium becomes much more un- 
stable, and the storm very likely develops into one of great 
fury. 

It is unstable because the cold air is resting on a layer of air that is 
specifically lighter, and when the latter is pressed upward it soon de- 
velops into a whirl. Winter cyclones are not confined to definite locali- 
ties, as are tropical cyclones, and in comparison with the latter their 
tracks are erratic. Their general direction is easterly, however. 

Land Storms. — The occasional local squalls excepted, 
all the storms of the middle and eastern United Stairs are 



CYCLONIC STORMS 



255 



cyclonic in nature, and except in violence they do not 
differ materially from the cyclones of the sea. In nearly 
every case they follow the same courses that are taken by 
the latter — westerly in tropical and easterly in temperate 
latitudes. 



In many cases a storm may originate at sea and end somewhere at 
a considerable distance inland, or vice versa. Many West Indian hurri- 
canes sweep into 
the Gulf of Mexico 
and thence into the 
Mississippi Valley. 
On the other hand, 
many north Atlan- 
tic storms begin far 
in the interior of the 
continent. In some 
instances storms 
originate in the Pa- 
cific, cross the Uni- 
ted States and the 
Atlantic, and finally 
disappear in the in- 
terior of Eurasia. 
Many of the cy- 
clonic storms of 
California and Ore- 
gon travel south- 
ward between the 
Coast Ranges and 
the Sierra Nevada 
Mountains. Per- 
haps they are dissipated in the arid region to the southward, but occa- 
sionally a cyclonic storm finds enough moisture to enable it to pass 
into the Mississippi Valley. 

Storm Tracks of United States. — Since the establish- 
ment of the various weather bureaus, the storm tracks 
have been closely studied, and it is found that most storms 




A STORM, OR AREA OF LOW BAROMETER 

The shaded part is the area of rain; the dotted region the ai 
oj cloudiness. The arrows fly with the wind. 



256 PHYSICAL GEOGRAPHY 

follow certain lines. In the United States two such tracks 
are apparent. The lesser number follow the trend of the 
Atlantic coast. These storms usually overlap the coast 
plain, but they seldom extend west of the Appalachian 
highlands. They belong to the class of West Indian cy- 
clones, originating in the Caribbean Sea, and turning 
northward, along the Middle Atlantic coast. 

Most of the storms form near the great highlands of the 
west — very frequently near the eastern base of the Rocky 
Mountains, crossing the continent in a northeasterly direc- 
tion. These storm tracks have a distinct tendency to shift 
north or south with the apparent motion of the sun, the 
belt being a little farther north in summer than in winter. 
The valley of the St. Lawrence River and the basin of the 
Great Lakes is a common track for summer storms. 

Characteristics of Land Storms. — Although they are 
sometimes accompanied by local thunder squalls, land 
storms rarely exhibit the fury of ocean cyclones. The area 
of the storm is usually larger, but the wind seldom attains a 
velocity greater than forty miles an hour. The storm 
centre is distinct, but the barometer may not fall more than 
half an inch. 

Clouds, and rain or snow accompany the majority of 
storms, but the area of rain does not always cover the 
whole extent of the storm; as a rule, most of the cloud 
area, and the rain as well, occur in front of the storm 
centre. As the latter passes there are occasional showers 
in which the rain falls vertically, or perhaps drives slightly 
toward the east. These an; the "clearing showers." 

Because the wind blows toward the storm centre, it is 
evident that storms of the second class will be preceded by 
easterly and will clear with westerly winds. Those from 



CYCLONIC STORMS 



257 



the West Indies will begin with northeasterly and clear 
with southwesterly winds — the nor'easters and sou'westers. 

Storms may be accompanied by thunder-showers, cold 
waves, tornadoes, and waterspouts. Thunder-storms and 
tornadoes are local in character, and often occur indepen- 
dently of general storms. Waterspouts and tornadoes are 
local, the former being confined to the water. Cold waves 
are general. 

Anticyclones. — Just as the trough of a wave of the sea 
is followed by the crest of another wave so, in the aerial 
ocean, an area of low barometer is followed by one of high 
barometer. The latter is 
practically a descending, or 
downdraught of air, which 
flows outward at the bottom 
in every direction. 

The paths along which 
anticyclones move are not 
materially different from cy- 
clone paths; that is they 
each follow an easterly track 

in the wake of a cyclone. The whirl, however, is in the 
opposite direction, being from west to east, corresponding 
to the movement of the hands of a watch, lying face up. 
On the eastern side of the anticyclone the air is apt to be 
dry and cold; on the west side, dry and warm. 

Cold Waves. — In many instances the barometric pressure 
is much higher on one side of the storm track than on the 
other. If the bank of air lies north, or northwest, its 
temperature is pretty apt to be low, and the depression 
will fill with cold air, forming a cold wave. Many winter 
storms are followed by cold waves, and a body of air whose 




CLEARING WEATHER CLOUDS 



258 PHYSICAL GEOGRAPHY 

temperature is much below the freezing point will flow 
as far south as the Gulf coast. To this form of cold wave 
the destruction of the Florida orange groves is due. 

Occasionally the wind blows with a velocity of sixty 
miles an hour or more, carrying fine snow and ice crystals. 
These anticyclonic winds are blizzards. They are very 
severe in upper Mississippi Valley, and are the most de- 
structive storms that sweep the cattle ranges. 

The blizzard was first noted in the records of an exploring party 
which, in 1747, wintered on the shores of Hudson Bay, at a place now 
called York Factory. The name was introduced as a technical name 
into the weather service in 1876. The blizzard of January, 1888, is 
an example of the effects of the translation of cold air from the extreme 
north. At Helena, Montana, the temperature fell fifty degrees in four 
and one-half hours, and sixty-four degrees in less than eighteen hours. 
At Crete, Nebraska, the thermometer fell eighteen degrees in three 
minutes. This wave covered almost the whole United States, carrying 
freezing weather into Florida, California, and southern Texas. In 
March, 1S87, a cold wave, extending along the valley of the St. Lawrence 
River, was marked by a fall of temperature ranging from fifty to seventy- 
one degrees in twenty-four hours. In Denver, January 15, 1875, 
there was a drop in temperature of forty-eight degrees in one hour. 
Practically, the northern limit of the torrid zone in the United States 
is the southern limit of the cold wave; this line crosses the southern 
parts of Florida and Texas. 

Warm Waves. — On the other hand, if the bank of air 
is on the south side of the storm track, the mass of air 
drawn from the south is very apt to be warm and very 
moist. Under such conditions a warm wave results. 
Although the difference between the temperature warm 
waves and normal weather is not so great as that between 
cold waves and normal weather, yet the former are far 
more fatal. In all the densely populated parts of the 
country the advent of a warm wave is marked by an enor- 
mous increase in the death-rate. 



CYCLONIC STORMS 



259 



During several warm waves that, in July, 1881, covered the Missis- 
sippi Valley, there were more than one thousand deaths from sunstroke 
- — probably a greater number than have resulted from the cold waves 
of a score of years. Warm spells may result also from settled con- 
ditions, and not disturbances. The air resting upon a given area may 
not be disturbed in the course of several days. Its warmth therefore 
increases, and may become intolerably hot. 

Tornadoes. — Tornadoes are whirling storms of the 
land. Though they cover an area smaller than that of any 
other storm, they are 
probably the most vio- 
lent atmospheric dis- 
turbances known. The 
path of the tornado sel- 
dom exceeds thirty or 
forty miles in length, 
while the destructive 
part of the whirl is not 
more than a few rods 
in width. Like other 
cyclonic disturbances, 
the tornado is formed 
in an area of low barom- 
eter. Seen at a distance 
of one or two miles, it 
appears as a dense, 
black, funnel-shaped 




A TORNADO TRACK 

The position and direction oj the rails show the 
direction of the whirl. 



cloud hanging from rapidly whirling clouds above. The 
funnel is the centre of the storm, and so rapid is the whirl 
that it forms almost a vacuum. The rotary velocity of the 
wind is thought to benot far from two miles a minute. 

Between the terrific wind and the vacuous centre, noth- 
ing can withstand the force of the tornado. The stout- 



260 PHYSICAL GEOGRAPHY 

est tree-trunks are twisted as though they were ropes, 
and in many instances pulled clear out of the ground. 
Buildings in the way of the funnel cloud burst into pieces 
outwardly the moment the latter envelops them; heavy 
locomotives are lifted from the railway track; and iron 
bridges are blown from their foundations, twisted into 
shapeless tangles, and carried long distances. Another 
noticeable feature is the lane or "windroad" made when a 
tornado passes through a forest. 

The study of several hundred tornadoes has shown the 
manner in which they originate. At the beginning of a 
storm it sometimes happens that a great volume of cold, 
dry air lies on one side of the disturbance, while a mass 
of warm, moist air lies on the other side. 

During the progress of the storm large volumes of cold 
air are whirled into regions of warm and moist air. Now, 
if the heavier cold air lies next the earth, no disturbance 
follows. But if it conies to rest on the top of a thick layer 
of warm air the case is different. There will result an 
updraught of warm air, and soon the tornado is in full 
vigor. 

In about ninety-five per cent, of the tornadoes studied 
the whirl accords with that of other storms in the Northern 
Hemisphere. Almost always they move from the south- 
west to the northeast. In nearly every instance the tor- 
nado track lies south of a general storm. 

Major-General A. W. Greely, U. S. A., formerly Chief of the Weather 
Service, notes twenty-five tornadoes, in which the aggregate damage 
reached the sum of $15,000,000, while the loss of life was nearly fifteen 
hundred people. Concurrent with a storm that on February 9, 1884, 
crossed the United States, there were sixty distinct tornadoes. On that 
day eight hundred people were killed, twenty-five hundred were wound- 
ed, and more than ten thousand buildings were destroyed. 



262 



PHYSICAL GEOGRAPHY 



The story illustrated in the accompanying cut is grewsome. The 
house was surrounded by a grove of trees. To the easl of the 1khi.sc 
the trees were felled and twisted from right to left; those west of the 
house were untouched. The house itself was demolished and the debris 
hurled into the creek-bed near by. When the tornado cloud swooped 
down upon the house, the family fled for their lives, but unfortunately 
in the wrong direction. At first they ran northward, a direction of 
safety. Then, one after another, they turned eastward — first a little 
girl, who was instantly killed; then an older boy and a girl, who were 

much bruised and 
partly stripped of 
their clothing. The 
mother ran directly 
into the whirl and 
was found crushed 
and dead against 
the trunk of a tree. 
The fat her. with the 
babe in his anus, 
had reached a place 
of absolute safety, 
but in his fright 
turned eastward 
and ran into the 
whirl. They were 
picked up by the 
thrown several hundred feet, and instantly killed. An inspec- 







N 




FATHER 
AND BABY/ 
* A 












A 






U./ 






s* BOy /V° 






b); 




.• 






w 


*\ 




/ 


;irl 


•> MOTHER 


E 




v: 




K, TC »C* 




4.-/ 


A, 
f 


HOUSE 

[MAIN BARTI 


Ap 






A? 




jF 


S 









wind, 



tion of the accompanying illustration shows that the safest path of 
flight is toward the northwest or the southeast; to the southwest or 
the northeast is one of the greatest danger. 

All parts of the United States are subject to tornadoes, 
but they are most prevalent in the central Mississippi 
Valley. West of the 102d meridian they are rare, because 
there is so little moisture in the atmosphere. They rarely 
occur in mountainous regions. 

Tornadoes are more frequent in summer than winter. 
The greatest number occur in May, and more occur in May, 
June, and July than during the rest of the year. They 



CYCLONIC STORMS 



263 



are more frequent in the afternoon than in the morning, 

and rarely occur at night. 
Waterspouts. — A waterspout is a whirlwind of the sea 

or other large body of water. The whirl is so rapid that 

the water is carried upward to fill the vacuous centre. The 

lower part of the waterspout 
is probably a nearly solid col- 
umn of water; the upper part 
is a rapidly whirling mass of 
spray. Waterspouts are most 
common in the region of cy- 
clone tracks 



—especially 

within the 
track of the 
Gulf Stream. 
It is usually 
asserted that 
the water 
which com- 
poses them is 
fresh. This is 
not always 

the case, however; in many instances it is salt-water. At the 
lower part, the column is not more than ten or fifteen feet 
in diameter; in the upper part it is whirled into a balloon- 
shaped cloud of spray several hundred feet in diameter. 

The white squall is similar in origin to the whirl that re- 
sults in a waterspout; in fact, it may properly be called a 
fair-weather whirlwind of the sea. It is sufficiently violent 
to whirl a considerable volume of sea-water into spray, 
but hardly strong enough to form a waterspout. 




EFFECTS OF A TORNADO 



264 PHYSICAL GEOGRAPHY 

Weather Forecasting. —Knowing the laws of storms it 
is not a difficult matter to predict weather conditions with 
considerable accuracy. In the temperate zones weather 
conditions originate to the westward or southwestward of 
the observer; in tropical regions, at the eastward. 

Except in the extreme southern part, where tropical 
storms are common in summer, the weather of the United 
Stairs is essentially of the westerly type. The storms move 
from the west or southwest, to (he east or northeast. 

The United States Weather Bureau was organized for 
the purpose 1 of protecting agriculture, navigation, and 
commerce by furnishing information of coming storms, 
dangerous coast-winds, threatening floods, cold waxes, and 
killing frosts. Scattered over the whole territory in 
selected locations are about six hundred observers who, 
twice a day, at the same actual time, observe temperature, 
barometric pressure, relative humidity, direction of wind, 
amount of rain or snow, etc. These results are telegraphed 
tn Washington and entered upon a weather map. 

Lines are drawn through localities of equal barometric 
pressure 1 , and also through localities having the same tem- 
perature. The former are isobars, the latter isotherms. 
In this manner areas of high, .normal, and low barometer 
are readily mapped and located. When the direction of 
the wind is plotted it will be found that it is everywhere 
blowing toward the area of low barometer. 

Twelve hours afterward, when a new set of observations 
is plotted, it will be found that the area of low barometer 
has advanced eastward with about the velocity of an or- 
dinary express train. With this information both the 
direction and the velocity of the storm can be forecast for 
the succeeding twenty-four hours. 




STORM CENTRE: FIRST DAY 




STORM CENTRE: SECOND DAY 



266 PHYSICAL GEOGRAPHY 

About ninety per cent, of the predictions may be verified 
and the number aetually verified is very close to the possible 
limit. Failure of verification is due to several causes — the 
sudden swerving of a storm from its track; the dissipation 
of a storm once formed; and the unforeseen development 
of a local storm. The shifting of a storm one hundred 
miles on either side of its predicted track may nullify the 
forecasts over a very large area. 

The Weather Bureau of the United States is now a part of the Depart- 
ment of Agriculture. Most of the European nations have established 
similar bureaus, and daily observations are made on all transatlantic 
steamships. So complete are these records that scarcely a storm oc- 
curs in the North Atlantic which is not followed and its path pre- 
dicted with a high degree of probability. Flags (or sometimes painted 
cylinders and cones) are displayed on public buildings in nearly every 
town in the United States and Europe. A square white flag denotes 
clear weather; a blue flag, rain or snow. Temperature is indicated by 
a triangular blue flag. Above the square flag it denotes higher tem- 
perature; below the square flag, lower temperature; its absence denotes 
no change in temperature. Whenever the temperature falls twenty 
degrees or more (sixteen degrees in the northern states), if the mercury 
sinks as low as 32° (F.), it is technically a cold wave, and its approach 
is indicated by a white flag containing a black square. It is commonly 
called the "black flag." A fifth flag is sometimes employed to indicate 
local storms. For the benefit of mariners a Monthly Pilot Chart for 
the North Atlantic is published by the United States Hydrographic 
Office. This shows storm tracks of the preceding month, and the posi- 
tion of ice, fog, floating wrecks, or "derelicts" and other obstacles, for 
the current month. 

QUESTIONS AND EXERCISES.— Why does the wind blow toward 
a low and away from a high barometer? 

Why do cyclonic movements of the wind move toward the west in 
tropical, and toward the east in temperate latitudes? 

Why does the water flowing out of a sink through a discharge-pipe 
at the bottom form a whirlpool? 

In the map at the top of p. 265, near what city is the centre of the 
storm? What is the direction of the wind at New Orleans and Baton 



CYCLONIC STORMS 267 

Rouge? — at St. Louis and Cairo? — at Chicago and Davenport? — at 
Duluth? — at Cheyenne? — in the greater part of North and South 
Dakota? 

Name one or two places at or near which the barometer is 29.5 
inches ; 29.7 inches ; 29.9 inches ; 30 inches. 

About how far has the storm advanced at the time of observation 
on the second day? 

Note the direction of the wind at Pittsburgh, Cleveland, Wilming- 
ton, N. C, Cincinnati, Indianapolis, Chicago, Springfield, 111., Mil- 
waukee, New Orleans, Mobile and Little Rock. 

The wind whirls warm, moist air from the p-outh to colder, northerly 
latitudes; what will be the effect on the moisture? — on the tempera- 
ture of the region over which the storm passes? 

In what position, with reference to the storm centre, is most of the 
rain, as indicated by the shading? 

Whence comes the air in the western part of the whirl — from 
northerly or from southerly regions? 

Will it probably be colder, or warmer? Why? 

Make a forecast for Cincinnati for each of the two days. 

Make forecasts for New York, Denver, and Chicago for the third 
day. 

COLLATERAL READING AND REFERENCE 

Greely. — American Weather — pp. 178-272. 

United States Weather Bureau. — Daily Weather Maps. 



CHAPTEK XV 

ELECTRICAL AND LUMINOUS PHENOMENA OF THE 
ATMOSPHERE 

Electricity is manifested chiefly by its effects; of its ac- 
tual nature but very little is yet known. The laws per- 
taining to it are fairly well known, however; like most of the 
other forces of nature, it is a most useful servant when under 
intelligent control. In the slender thread of the incandes- 
cent light and the carbons of the arc light it appears both 
aslightand intense heat. Passing through insulated copper 
wire that surrounds a core of soft iron, it converts the latter 
into a magnet, and thus harnessed' it becomes a generator 
of great power. Electrical energy seems to be a form of 
motion, and it may be produced by motion. It is manifest 
not only in the earth and the air, but in space as well. 

Fundamental Laws. — The laws of electrical energy are 
not difficult to understand. A pith-ball, hanging by a silk 
fibre, and brought near a piece of dry and clean hard rubber 
that has been rubbed by flannel will at first cling to the 
hard rubber and then will fly away from it. If another 
ball, electrified in a similar manner, be brought near the 
first one, the two will repel each other. If, however, the 
second pith-ball be electrified by a piece of glass rubbed 
with silk, the two balls will then attract each other. 

Such an experiment demonstrates the principal laws of 
electricity. Bodies similarly electrified repel; h<><!irs <lij- 
jerenlly electrified attract one another. The electricity de- 

268 



ELECTRICAL AND LUMINOUS PHENOMENA 269 

veloped when glass is rubbed with silk is called positive; 
that produced by rubbing vulcanite with flannel, negative. 
Electricity passes quite freely through metallic sub- 
stances, which are said to be conductors, but with difficulty 
through such material as silk, wool, gums and resins, dry 
wood, and dry air, which are non-conductors. When, 
however, the electric force is so great that it will pass 
through these it is said to have a high potential, just as 
steam confined within a boiler is at high pressure. The 
"sparks" produced by rubbing sealing wax or vulcanite 
with flannel are of moderately high potential. 

The potential of electricity may be also likened to pressure on water 
flowing through a pipe. If the pressure be low the water will flow 
quietly through the pipe and fall at no great distance from the end of 
the nozzle; on the contrary, if the pressure be great, it will be projected 
a distance corresponding to the force. In a single cell of galvanic 
battery the potential, about one or two volts, is so low that the electricity 
will not jump across a space of one thousandth of an inch; the quantity, 
moreover, is very small. In an electric-light wire a current of con- 
siderable volume will leap across a space one- tenth of an inch or more ; 
its potential is about 1,000 to 1,500 times as great as that found in a 
cell of an ordinary galvanic battery, being from 2,000 to 5,000 volts. 
A good frictional electric machine will cause sparks to leap between 
points ten or twelve inches apart; the potential is very high, but the 
quantity is small. During a thunder-storm a stroke of lightning may 
jump a distance of a mile. Not only is the quantity enormous, but the 
potential is so great as to be immeasurable by ordinary standards. 

Electricity of the Air. — To the electricity of the air and 

the earth many of the most marvellous phenomena are 
due. In the simplest form we see its effects when tiny 
sparks result from rubbing the long knap of woollen cloth 
or the fur of an animal pelt; we see its grandest effects when 
flashes of lightning forge across the sky. The electricity 
of dry air is usually of high potential. Next the earth, 
however, the electricity of the atmosphere is not commonly 



270 PHYSICAL GEOGRAPHY 

noticeable, especially if the air is moist. The moisture is 
so good a conductor that the electricity is in a condition 
of equilibrium. At considerable elevations, or when the 
air is very dry, its presence becomes marked. The hair of 
the head crackles as a comb is drawn through it, and tiny 
sparks are given off when woollen clothing is rubbed. In 
the dry summer climate of deserts, the hair of horses' tails 
stands out like bushes,'and their manes are like fright wigs; 
sparks half an inch long may be drawn from a metallic 
body insulated from the ground. 

Ordinarily, the electricity of the air is positive, but, with 
much moisture present, it may be negative. Just before 
the beginning of a gentle shower it often becomes negative, 
and during a heavy storm it frequently changes from posi- 
tive to negative and vice versa very rapidly. In such cases 
the character of the electricity may vary in different places; 
that is, it may be positive at one locality and negative at 
another, only a few miles distant. 

At different localities, the character of the electricity may be so very 
unlike, that the earth currents are sufficient to operate telegraph wires 
without the aid of the batteries. In regions of dry climate such con- 
ditions are more frequent than in localities where the air is moist. 

Neither physical nor chemical change in a substance 
takes place without the development of electric energy. 
Friction likewise is a potent factor in its generation. The 
flowing of water; the chafing of the winds against the 
earth's surface; even the friction of the air against itself 
produces it copiously. Evaporation and condensation also 
produce it; and inasmuch as an enormous amount of the 
vapor of water is constantly vaporized at one locality to 
be condensed at another, evaporation and friction may be 
regarded as the chief agents in its production. 



ELECTRICAL AND LUMINOUS PHENOMENA 271 

The vapor of water is not only a good conductor of electricity, but 
it is an excellent storage reservoir as well. The small globules of vapor 
that compose the cloud mass carry the charge of electricity each upon 
the surface. But when a great number of these globules are condensed, 
to form a drop of water, the surface of the drop is infinitely smaller 
than the aggregate surface of the globules. The potential of the 
drop, in comparison with that of the globules, is enormously in- 
creased. If an electrified body, such as a vulcanite rule, is brought 
near a sprayer or a sprinkler the fine spray immediately gives place 
to large drops. 

Since these agents are always at work, electricity is being 
constantly generated. But the electricit}^ of the air and 
that of the earth are unlike; the two, therefore, neutralize 
each other. If the air be moist the two kinds of electricity 
readily pass from the earth to the air, and from the air to 
the earth, until the equilibrium is restored. This trans- 
ference goes on so quietly that there is no great accumula- 
tion of electricity. It is only when the air is very drjr, or 
during an electrical storm, that the transference takes place 
with difficulty. 

Thunder-Storms. — When clouds are present in the air, 
however, there is often an enormous accumulation of 
electricity, either within or upon their surface, and the 
transference or exchange, therefore, may become violent. 
Such disturbances are thunder-storms. 

When large masses of cloud hover over the earth it 
sometimes happens that they are differently electrified. 
Under such circumstances the two clouds are mutually at- 
tracted. The potential is very high and the transference 
takes place in the form of great flashes of lightning. Usually 
the interchange takes place between the two clouds, but 
quite as frequently it is between the clouds and the earth. 
The form of lightning varies. The interchange takes place 
always along the line of least resistance, and as this is 



272 PHYSICAL GEOGRAPHY 

seldom, if over, a straight line, it has taken the name, 
zigzag lightning. 

The flash of light that accompanies the electrical discharge heats 
to whiteness the foreign matter in the path of the discharge. The air 
being a poor conductor offers considerable resistance to the passage of 
the electricity, and is therefore intensely heated along the line of dis- 
charge. The thunder is produced in exactly the same" manner as is the 
noise that accompanies the discharge of a firearm. The air at the 
point of discharge is rarefied almost to the extent of being a vacuum; 
the rush of air to fill the vacuum is the thunder. The rumbling of the 
thunder is due partly to echo and reverberation, and partly to the fact 
that the sound along the line of discharge reaches the ear at different 
intervals — the greater the distance the longer the time required fur the 
sound to reach the ear. 

In paintings and illustrations it has always been customary to depict 
the electric discharge in the form of a zigzag line of many sharp angles. 
In the past few years photographs of the lightning stroke have been 
successfully made. One of these on the following page shows the fallacy 
of former notions on the subject. 

Another form is known as sheet lightning. This inter- 
change takes place, not along a line, in the form of a " bolt, " 
but simultaneously over a large area. The discharge is qoI 
attended by a crash of thunder, nor by a blinding flash of 
light. On the contrary there is nothing but a quivering 
glow that lasts sometimes for eight or ten seconds. A 
sheet lightning discharge takes. place usually between the 
earth and the clouds. The electricity is of low potential 
and therefore not destructive. This name is also applied 1<> 
flashes of lightning that, occurring at a considerable dis- 
tance, are reflected from the under surfaces of clouds. 

This reflection is also called heat lightning. It is rarely observed 
except at the horizon when the latter is overcast by clouds. The re- 
flected flashes of light are usually so fur away that the accompanying 
thunder is not heard. Still another form is commonly called bull 
lightning. Of this kind of discharge but little is known, and although 



ELECTRICAL AND LUMINOUS PHENOMENA 273 

its occurrence has been alleged for more than two hundred years, its 
existence is somewhat in doubt. 

Occasionally the discharge takes unusual forms. Among 
them, but rare in occurrence, is the phenomenon known as 
St. Elmo's fire. This discharge, though best known at sea, 
is also occasionally observed on land. At the time of its 
occurrence there is usually a considerable electrical disturb- 
ance though not necessarily a thunder-storm. Owing to 




LIGHTNING 

From an instantaneous -photograph by W . F. Cannon. 

the feebleness of the light emitted, it is not frequently 
noticed in the daytime. It consists of a pale, shimmering 
light, at the tips of the yards and spars of a ship's rig- 
ging, or from the branches of trees. The glow lasts for a 
few moments and then disappears. It is probable that the 
St. Elmo's fire is identical with the bluish glow that is seen 
when a frictional electrical machine is worked in the dark — ■ 
a phenomenon commonly known from its shape as the 
"brush" discharge. 



274 PHYSICAL GEOGRAPHY 

While Ca?sar was carrying on his military operations in Africa, he 
relates that, during a severe hail-storm, the spears of his fifth legion 
were tipped with fire. The phenomenon was undoubtedly identical 
with that of St. Elmo's fire. It is not improbable that the "ignis fatuus," 
"Jack o' lantern," or "Will o' the wisp "is a similar electric phenomenon. 
This is a hazy indistinct light occasionally seen in swamps. According 
to tradition, the ignis fatuus is a bright light that moves rapidly from 
place to place mainly for the purpose of alluring unsuspecting travellers 
into dangerous places. As a matter of fact it is practically motionless. 

In some instances a thunder-storm passes along a path 
a thousand miles long, spending its energy and disappearing 
when the electrical equilibrium is restored. It may also 
move along at the front of an air current. The centre of 
energy is marked by a brisk cyclonic movement, and as the 
storm progresses along its path the area gradually in- 
creases. The conditions of formation are not unlike those 
which result in tornadoes. Like them, progressive thuin ler- 
storms occur usually on the south side of a general storm, 
and there are apt to be several of them following in quick 
succession. The progressive motion varies from fifteen to 
about fifty miles an hour. 

The Aurora Borealis. — The magnificent display com- 
monly called the "northern lights," is an electrical phenome- 
non similar in appearance to the "brush" discharge. It 
is most common in high latitudes, though it is occasionally 
observed between latitudes 30° and 40° N. In appearance, 
the aurora is an arch of light stretching across the sky fifteen 
or twenty degrees above the horizon. It has a tremulous 
motion, and the upper streamers sometimes mount to the 
zenith. 

The aurora is not confined to northern regions; it occurs in southern 
circumpolar regions as well. In the southern hemisphere, boweverj 
it is called the aurora australis, but the southern aurora is neither BO 
brilliant nor so frequent in occurrence as that of the northern regions. 



ELECTRICAL AND LUMINOUS PHENOMENA 275 

It must not be thought that the aurora occurs at night-time only; 
it may take place at any time — day or night. It is not visible in day- 
time, however, on account of the greater brilliance of the sun. 

In color the aurora varies between pale green and crim- 
son. Sometimes it closely resembles a green curtain edged 
and lined with gold. Auroras are most frequent during 
sun-spot periods; they are usually coincident with mag- 
netic storms also. In circumpolar regions, at times, they 
are almost constant in occurrence,? The cause of auroras 
is not with certainty known, but they are thought to be an 
exchange between the electricity of the atmosphere and 
that of the earth. The arch of the aurora nearly always 
surrounds the earth's magnetic pole. 

Professor Balfour Stewart has advanced the opinion that both auroras 
and earth currents are secondary currents due to small but rapid changes 
in the earth's magnetism. The body of the earth may be compared 
to the magnetic core of an induction coil, the lower strata being the 
insulating medium, while the upper strata, which are much better con- 
ductors, take the part of a secondary coil. 

Magnetism. — A bar of steel, iron, or nickel, or a piece 
of lodestone that has the property of attracting and hold- 
ing to its surface small pieces of similar metals is called a 
magnet. Steel retains its magnetism permanently, and for 
all practical purposes the magnet is a flat bar of polished 
steel, eight or ten inches in length. Sometimes, however, 
it is bent into a U-shapecl form called a horse-shoe magnet- 

When a bar of steel is magnetized, it is found that the 
magnetic force is not uniformly distributed throughout the 
bar, but is most intense at the ends. These are the poles 
of the magnet; they are designated as positive +, and 
negative — , according to the direction they take when the 
magnet is suspended at the centre of gravity. The north- 



276 PHYSICAL GEOGRAPHY 

pointing end is usually marked — ; the south-pointing end 

is rarely marked. 

A slender bar of ordinary steel suspended by a silk fibre 
from its centre of gravity, will lie indifferently in any 
direction in which it is placed. If the bar be magnetized, 
however, it takes new properties. It no longer remains in- 
differently in any position; it swings to a direction thai is 
nearly or quite north and south. It no longer remains 
balanced, but the north-pointing end dips toward the earth. 

If now another bar magnet be brought near it, the latter 
shows no little sensitiveness. If the + end of the bar be 
presented to the + end of the suspended magnet, the latter 
will instantly turn away; if the two — ends be brought to- 
gether the same thing will be noticed. On the contrary if 
+ and — poles be brought together they are strongly at- 
tracted. From these experiments the laws of magnetism 
are deduced. Like magnetic poles repel; unlike poles at- 
tract. Either pole of the magnet, however, will attract 
alike an unmagnetized piece of iron or steel. 

It is upon these laws that the science of navigation by 
the compass depends, for the earth behaves as a magnet 
and the essential part of the mariner's compass is also a 
magnet. 

Magnetic Variation. — The earth's magnetic poles are 
not situated at the geographical poles. The magnetic n< >r1 1 1 
pole is situated west of Boothia Land, a few miles north 
of the crossing of the 97th meridian and the 70th parallel. 
Its position is not fixed, and it is moving in a westerly di- 
rection. The position of the magnetic south pole is not 
known, although roughly approximated. 

The shape of the earth is not such that its magnetic force can possess 
much intensity. Several magnetic poles are known to exist, hut only 



ELECTRICAL AND LUMINOUS PHENOMENA 277 



the two north poles of great intensity are usually charted. The pole of 
greatest intensity is the one commonly known as the magnetic north 
pole. Since its discovery by Ross, it has moved about forty miles west- 
ward. In 1879 it was approximately located by Lieutenant Schwatka 
in the open space between Victoria and Franklin Straits. Its exact 
position has not been determined since 1831, and it is doubtful if its 
location at that date was so precise as might be inferred from the figures, 
which are expressed in minutes of arc. At that time there were no 
instruments sufficiently delicate for such precise determination. In 
1884 the position of this pole was again approximately determined to 




LINES OF EQUAL MAGNETIC VARIATION 

be in lat. 70° 30' N.; long. 96° 40' W. The position of the magnetic 
south pole was also approximately determined in 1905. 

Observations made at Paris on the movement of the magnetic north 
pole cover a period of more than three hundred years. In 1580, the 
declination at the city was 11° 30' E. It decreased until in 1683 it 
was nothing, after which time the variation became west. The westerly 
variation increased until, in 1814, it amounted to about 22° 30' W. 
Since that time it has dropped to about 22°, and, it is thought, is slowly 
decreasing. In 1790 the variation at Norfolk, Va., was nothing; in 1893 
it was about 3° 16' W. In New York City the variation in 1686 was 
9° W.; in 1790 it had decreased to 4° 15' W. ; after this time, however, 
it gradually increased until, in 1907, it was about 9° 26' W. 



278 PHYSICAL GEOGRAPHY 

Because the magnetic poles are not situated at the geo- 
graphic poles, it is evident that the magnetic needle can 
point due north and south in but few places. In the ac- 
companying chart, a heavy black line passes through 
these points. This line, called the agonic, is the line of 
no variation. West of this line the north-pointing end of 
the needle turns toward the east, and east of it it swerves 
to the west. Along each of the lighter lines the needle 
has the same deviation at all points, and these lines, there- 
fore, are called isogonics or lines of equal variation. This 
deviation from the true meridian is called declination. 

Besides the force that causes the needle to take a north-south direc- 
tion, there is another that causes it to dip or incline one end toward 
the earth. This is called the vertical force, or inclination. Along 
an irregular line passing around the earth, sometimes north of the 
equator and sometimes south of it, the needle has an absolutely horizon- 
tal position. This is the magnetic equator or aclinal. North of this 
line the north-pointing end dips toward the earth. The farther the 
observer goes northward, the stronger becomes the vertical force, and 
when the magnetic north pole is reached the needle has a vertical 
position, the — pole being next the earth. 

South of the aclinal, the conditions are reversed. The + pole 
dips more and more, until, at the magnetic south pole, the needle is 
again vertical with the + pole next the earth. A line on which the 
dip is everywhere the same is called an isoclinal. 

Not only does the position of each isogonic vary from 
time to time, but the rate of variation is not uniform; even 
at the same place the rate varies from year to }^ear. In 
the northwestern part of the United States the yearly va- 
riation is at present from 3' to 7'; in the southwestern 
part it is, at present, nothing; in the eastern and central 
parts it varies from 3' to 5'. 

The deviation from the true geographical meridian also 
varies from day to day. Most of these variations are 



ELECTRICAL AND LUMINOUS PHENOMENA 279 

periodical. Some are daily, some monthly, and some 
yearly; they are probably caused by the daily rotation of 
the earth, the passage of the moon, and the annual motion 
of the earth. There are also irregular changes in variation 
which cannot be accounted for. 

Such changes in variation are rarely great; in temperate and in low 
latitudes they cannot well be detected except by close measurements. 
In the vicinity of the magnetic pole, however, they are more marked. 
At Point Barrow and at Lady Franklin Bay, during a period of twenty- 
four hours, a change of nearly eleven degrees was recorded. 

In order to study these variations, magnetic observatories have been 
established in various parts of the world. The essential part of such 
an observatory is a series of magnets each carrying a small mirror, 
mounted in such a manner that a spot of light is thrown on a sheet of 
photographic paper. The sheets of paper are fastened each to a cylinder 
revolved by clockwork, so that the "spot of light draws a photographic 
line along the whole length of the sheet in twenty-four hours. If the 
magnet were motionless the line would be straight, but if the magnet 
turns even a small fraction of a minute, the spot is thrown out of posi- 
tion and the line becomes irregular. Usually three magnets are em- 
ployed — one to measure variations in horizontal force; one for varia- 
tions in vertical force ; and one to measure the strength of the horizontal 
force. 

Magnetic Storms. — Not infrequently the irregular vari- 
ations of the needle are so violent that they have been 
called magnetic "storms," and during the progress of one 
of these disturbances the needle is in a constant tremor. 
Magnetic storms seem to be closely associated with the 
spots that at times are visible on the surface of the sun; 
but they are doubtless due to electrical storms also. The 
sudden formation or change in the position of a sun spot 
is nearly always attended by great magnetic disturbances. 
The period when they are most frequent, moreover, cor- 
responds to the period when sun spots are most numerous. 

This period recurs every eleven years. In 1882 the formation of a 
sun spot was attended by a magnetic storm that was recorded at Point 



280 PHYSICAL GEOGRAPHY 

Barrow, Lady Franklin Bay, Los Angeles, Kew (London), Cape Horn, 
and Paris. Telegraph instruments were affected, and in some instances 
long circuits were worked by ground currents. At the magnetic ob- 
servatory then in Los Angeles, California, the tremor of the magnets 
was so great that for several hours one of the instruments failed to 
make a legible record. 

The Mariner's Compass. — The compass is a slender 
bar of magnetized steel, so constructed as to baltnce on a 
pivot and turn freely upon it as well. Usually it is armed 
with a sliding weight, so adjusted that it exactly counter- 
balances the dip or vertical force, thereby keeping the 
needle in a horizontal position. 

On land the compass is of but little practical use except 
in rough surveys. On the sea, however, it furnishes the 
only means by which a vessel may be kept continually on 
her course. For this reason the mariner's compass is 
constructed with the greatest care and precision. The 
needle, which consists of one or more slender bars of steel, 
is fastened to a circular card subdivided into thirty-two 
parts, on which are printed the cardinal directions. These 
are called points of the compass. The compass box is 
mounted on gimbals, so that, no matter what may be the 
motion of the vessel, the box always retains a horizontal 
position. 

In the Ritchie compass, now generally used in the United States 
Navy, the compass box is filled with alcohol in which the card and 
needle almost float, the object being to relieve the bearing of the weight 
of the card, and thus make the needle more sensitive. The compass of 
Sir William Thomson (Lord Kelvin) consists of a battery of six or 
more very slender magnets held in a skeleton frame. The latter is 
so light that the friction on the bearing is imperceptible. This compass 
is used in the English Navy, and by most of the transatlantic liners. 

The use of steel in the construction of vessels has added materially 
to the difficulties of sailing by compass. The hull of a steel or iron 
vessel has poles of intensity peculiar to itself, and these are apt to change 



ELECTRICAL AND LUMINOUS PHENOMENA 281 



in time, so that frequent tests of the compasses are necessary. There 
are various devices for obtaining the proper correction for the compass 
on steel vessels; a very effective method is to swing the vessel, stem and 
stern, along a geographic meridian and then compare the observed 
with the normal variation. On battle-ships either the addition or the 
removal of the armament, or the substitution of a steel for a wooden 
mast, is apt to make readjustment of the compasses necessary. 

Along nearly every travelled ocean route, the variation 
of the compass changes day by day. On the regular routes 
of the transatlantic liners, 
the variation increases 
from about nine degrees 
at New York to more 
than thirty-five degrees 
at the crossing of the 
40th meridian. It then 
decreases to about twenty 
degrees at Liverpool. 

In arctic regions, where the 
horizontal element of force is 
so weak, and the dipping force 
so strong, sailing by compass 
is a very difficult matter. Not 

only does the variation change rapidly over short courses, but the 
needle becomes exceeding sluggish. On whaling vessels it is customary 
to attach a line to the compass box so that the steersman, by occasional- 
ly shaking it, may better judge the course over which the vessel is sailing. 

Luminous Phenomena. — Transparent though the at- 
mosphere seems, not all the light transmitted passes through 
it. Rays of light are not only refracted, or bent out of the 
direction in which they started, but possibly they are de- 
composed. The distortion that one may observe by look- 
ing at an object across the top of a very hot stove, or a 
chimney is an example of refraction. On the other hand, 




MARINER'S COMPASS 
An ordinary pattern. 



282 PHYSICAL GEOGRAPHY 

the color effects observed when light passes through a glass 
prism, such as a chandelier pendant, or even the bevelled 
edge of plate-glass, are examples of decomposition. 

A ray of light striking a polished surface is reflected, 
rebounding in the same manner as does a rubber ball thrown 
against the floor. The same thing may occur when the ray 
strikes the surface of water, or even that of a layer of air. 

The air contains innumerable dust motes and particles 
so fine and light that they seem always to float. This is 
seen when a few rays are admitted into a darkened room; 
their passage is marked by the light reflected from the 
motes; a part of the light therefore is scattered, or dis- 
persed. 

White light is a mixture of all the rainbow colors. Or- 
dinarily the blue and violet rays are the more easily scat- 
tered by the dust motes of the atmosphere. Being reflected 
to our eyes they give to the sky its blue color. At times, 
however, when the air is heavy with dust, the sky may 
acquire a hue that is distinctly red. This was very notice- 
able in 1883, after the eruption of Krakatoa; for nearly a 
year the sunsets were exceedingly lurid. At sea, the blue- 
ness of the sky is very marked, and the color is purer than 
on land; with accumulating moisture, however, it may 
acquire whitish tints. At very great elevations the blue 
gives way to a purple-black hue. 

Mirages. — When a layer of light air rests on another 
that is heavier, the surface of contact often reflects much 
light. If the surface is a little lower than the eye of the 
observer, the reflection of the sky much resembles that of 
a surface of water, and a mirage results. In deserts and 
arid regions, the illusion is so perfect that nothing but 
experience will enable one to distinguish the mirage from a 



ELECTRICAL AND LUMINOUS PHENOMENA 283 

lake. The "lake" mirages of the Colorado Desert have 
lured both cattle herds and travellers to their death. 

With the reflecting surface above the eye, the character 
of the mirage differs. Thus, at times, off the lake shore 
at Chicago, one may see the lighthouse and the shipping at 
the mouth of the river inverted in the air. 

In many instances, however, the rays of light may pass 
through layers of air that differ greatly in density. In 
such cases the light rays are so much refracted that dis- 
torted or blurred outlines of an object result. Some land 
mirages are of this character. 

It sometimes happens that the rays of light reflected 
from an object, are refracted so that they are curved 
slightly toward the earth, and a distant object that other- 
wise could not be seen is brought to view. This phenome- 
non occurs at times along the Mediterranean and Red Seas, 
and it is not unknown along the Great Lakes. As a rule, 
a dry, still atmosphere is essential to the formation of the 
mirage. 

Coronas and Halos. — The ring or rings about the sun 
or the moon are very common phenomena. The small 
rings are coronas; the larger ones, halos. In the corona, 
which is not very common, there is usually a series of con- 
centric, colored rings. These, it is thought, result from a 
scattering of the light by the moisture of the atmosphere. 
The halo of the moon appears when the air is very moist. 
For this reason it is apt to portend rain or snow. 

The halos of the sun are associated usually with cold 
weather. They are thought to result from the refraction 
of the light as the latter passes through the ice crystals of 
cirrus clouds. Frequently there are several circles. Some 
of them are concentric; some are tangent one to another; 



284 



PHYSICAL GEOGRAPHY 



and others intersect one another. At the places of inter- 
section and of tangency more light is radiated, and 
these spots, which are very bright, form sun dogs, or mock 
suns. 

Rainbows. — During a summer shower, when the sun 
breaks through a rift in the clouds, the light passes through 
the falling drops of water in such a way that it is not only 
refracted but decomposed. The resulting decomposition 




HALOS OBSERVED BY GENERAL GREEL.Y 



is the arch of colored light that constitutes the rainbow. 
The bow is blue and violet on the inner, and red on the outer 
side. Sometimes there is a larger secondary bow in which 
the order of colors is reversed. 

The rainbow is best observed when the sun is near the 
horizon. The observer sees the bow when his back is 
turned toward the sun. The rainbow is observable in the 
spray of waves, and also in the spray of cascades. 



ELECTRICAL AND LUMINOUS PHENOMENA 285 

QUESTIONS AND EXERCISES.— Verify the statements concern- 
ing the mutual attraction and repulsion of electrified bodies, observing 
the directions on p. 268. 

Verify the statements noted on p. 275, using one or more stout knit- 
ting-needles and strands of untwisted silk. For observing inclination 
the strand of silk may be fastened by a slip knot to the needle ; for the 
other experiments the needle may be thrust through a bit of paper 
held by the silk. In magnetizing the needles, rub the ends only. 

From the chart, p. 277, estimate the magnetic variation of the place 
in which you live. 




RAINBOWS: PRIMARY AND SECONDARY 

The dolled lines show the rejraclion and reflection of the light. A is the primary, B the 
secondary bow. 

At any time of their occurrence note carefully whatever you may 
observe with reference to auroras, mock suns, halos, and coronas. 

Occasionally, in very dry weather the disc of the sun is considerably 
distorted at the time of setting; explain why. 

The sun and the moon seem to be much larger when near the 
horizon than at zenith; is this phenomenon real or apparent? The 
use of a paper or other tube an inch or two in diameter will aid in the 
solution of this question. 

Explain the phenomenon of the " sun's drawing water." 



COLLATERAL READING AND REFERENCE 

Waldo. — -Elements of Meteorology, pp. 166-180. 
Greely. — American Weather. 
Davis. — Elements of Meteorology. 



CHAPTER XVI 

CLIMATE AND ITS FACTORS 

The conditions of a region with reference to its habita- 
bili'ty constitute its climate. These, in general, are the 
results of heat and moisture; and climate, therefore, in- 
cludes all the modifications due to heat and cold, rain and 
drought. Climate is modified by latitude, altitude, position 
of highlands, direction and prevalence of winds, and the 
inclination of the earth's axis. 

To these may be added the effect of ocean currents. Cold currents 
carry water into warmer latitudes, and cause fogs that sometimes 
cover large areas. Warm currents flowing into the coves and bays 
of arctic coasts keep the harbors free from ice. 

Latitude. — Latitude affects climate chiefly with refer- 
ence to temperature. The greater the distance from the 
equator, the lower will be its average temperature. The 
sun's rays are never vertical beyond the tropics, and in 
polar regions they fall so obliquely that they impart but 
very little heat to either land or water. Illustrate this by 
means of the diagram on p. 295. 

In going from equatorial to polar regions one will pass 
through every degree of warmth from perpetual summer to 
the coldest winter. Within thirty or thirty-five degrees 
of the equator the change in temperature is not great, but 
beyond the forty-fifth parallel the winter climate grows 
rapidly colder for every few degrees of increase. 

Latitude also exerts an influence on rainfall. As a 
rule, the rainfall is greatest within the torrid zone. The 

286 



CLIMATE AND ITS FACTORS 287 

equatorial cloud belt is a zone of ascending air currents, 
and the air being chilled by its expansion, the moisture is 
condensed, and there is an almost constant fall of rain. 
The cloud belt is therefore a rain belt, and it swings from 
tropic to tropic with the apparent motion of the sun. In 
the region of tropical calms, on the contrary, the rainfall 
is deficient. These calms are regions of descending currents 
of the air, and the air being warmed instead of chilled by 
its descent, becomes relatively dry. 

Altitude. — The effect of altitude is much the same as 
that of latitude. The temperature, is lower by about one 
degree for every three hundred feet of ascent. Thus, one 
may find on the slope of a highland all the intermediate 
degrees of temperature between summer and winter. In 
Mexico the effects of altitude are finely illustrated. The 
city and seaport, Vera Cruz, is intolerably hot and moist; 
less than two hundred miles away, the City of Mexico, at an 
altitude of 7,000 feet, enjoys a climate that is cool and in- 
vigorating; while the top of Orizaba, about 18,000 feet 
high, is snow covered. 

A striking example occurs in the plateaus of the Colorado River. 
Hurricane Ledge forms the boundary between two plateaus. On the 
upper mesa the products are those of a temperate climate; in the 
lower they are sub-tropical. 

At high altitudes the difference between the temperature of day and 
night is very great. Thus on Mauna Kea, Hawaii, midday tempera- 
ture frequently runs above 100° F., while the night temperature may 
be below the freezing point. Observations taken by the aid of balloons 
show that at the altitude of 40,000 feet the temperature varies from 
about - 60° to - 80°. Above 4,000 feet in the air there is but little differ- 
ence between the shade temperature of the day and that of night. 

Position of Mountains. — High mountain-ranges often 
control the quantity of rain falling on the surface of a 



288 PHYSICAL GEOGRAPHY 

region. In tropical latitudes rain-hearing winds blow 
from the east; the eastern slope of high ranges is therefore 
well watered, while the western slope is dry. In the 
temperate zones, on the other hand, the rain winds are from 
the west; and the western slope in consequence receives 
most of the rain, while the eastern side is comparatively 
dry. Thus, in the Peruvian Andes, the rain winds deluge 
the eastern slope, leaving the western side a desert. In the 
southern Andes, the conditions are reversed; the rain falls 
on the western side while the eastern slope is arid. 

The effect of the absence of mountains is observable in 
Australia. Partly because of its latitude, but mainly for 
want of a high range, the greater part of the continent is 
a desert, and the rain falls on the highlands of the eastern 
side only. In the great African desert, the few isolated 
ranges receive considerable rain on their summits, but very 
little falls elsewhere. 

Distance from the Sea. — The proximity of the sea 
exerts a marked effect on climate, both with respect to tem- 
perature and moisture. The climate of a coast region is 
always more equable than that of a far inland or coniinculnl 
area. The reason therefor is apparent; the air over the 
ocean has a much more uniform temperature than that 
over the land. 



The result is seen when the extremes of temperature are noted. 
For example, San Francisco and Leavenworth, Kan., have nearly the 
same mean temperature for the year. But while the difference between 
the summer and winter temperature of San Francisco is less than ten 
degrees (F.), that of Leavenworth is almost fifty degrees. 

A noticeable and highly important difference between a maritime 
and a continental climate, is the daily range of te'mperature. In a 
maritime climate this rarely exceeds twenty degrees (F.), while in a 
few inland regions the fluctuations may be twice as great. 



CLIMATE AND ITS FACTORS 289 

Not all coast regions, however, enjoy a maritime climate. 
Because the winds of the temperate zones are, as a rule, 
westerly, on the eastern coast of such regions land winds 
are prevalent. The coast region of the northeastern part 
of the United States is an example. The same is also true 
of the northeast coast of China. Its climate is distinctively 
continental, and the influence of the sea penetrates only a 
very few miles inland. On the other hand, the climate of 
the southern part of South America is distinctly oceanic. 

The climate of oceanic islands is always equable. The 
Philippines and the Hawaiian Islands, although in the torrid 
zone, are regions of perpetual spring, with no excesses of 
temperature. The Leeward and Windward islands of the 
West Indian group are also examples. Though situated 
only a few degrees north of the equator their summer tem- 
perature is less oppressive than that of New York City. 

Prevailing Winds. — Winds are the chief medium for 
the transmission both of moisture and warmth. The Trade 
Winds modify the excessive heat of low latitudes, and warm 
winds blowing into high latitudes soften the rigors of the 
region into which they blow. The mild temperature of 
western Europe is due largely to southwesterly winds, 
and the same is true of the equable climate of western 
North America. Not only do the winds themselves trans- 
fer a great amount of heat by convection, but the latent 
heat of the water vapor furnishes an enormous supply. 
When the vapor, mingled with the wind, is carried to colder 
latitudes and there precipitated, all this heat is again set 
free. The chart of winds (p. 223) gives the information 
necessary to determine roughly the climate of a coun- 
try. The regions invaded by sea winds that have come 
from low latitudes are the regions of warm and equable 



290 PHYSICAL GEOGRAPHY 

climate. Inland and polar regions arc areas of climatic 
extremes. 

There are other minor factors that also determine the climatic con- 
ditions of a locality. Much cloud and fog prevent evaporation and 
therefore tend to equalize temperature. Evaporation tends to lower 
temperature because of the great amount of heat that becomes latent. 
The penetrability of water to heat is greater than that of rock; more- 
over, the capacity for heat of the former is about twice as great as the 
latter. All these facts tend to the greater equability of the water as 
compared with the land. 

Changes in Climate. — As a rule, the climate of a 
country does not change materially except after long in- 
tervals of time. The mean temperature of any given 
locality rarely varies more than a very few degrees from 
one year to another, and the averages of long periods show 
still less variation. Fluctuations in rainfall and cloudiness 
are considerably greater than those of temperature. In 
moist regions the rainfall of wet years may be nearly twice 
that of dry years; in localities of deficient rainfall the differ- 
ence may be greater. 

When time is reckoned by geological epochs, however, 
it seems certain that great climatic changes of a radical 
character have occurred in every part of the earth. The 
Glacial Epoch, already described, is an example of a change 
in the climate that took place in the North Temperate Zone. 
The rainfall of the Basin Region of the United States has 
been subject to periods of oscillation. The few scattered 
sinks and salt lakes of the Great Basin itself are remnants 
of two large lakes that existed there at no very remote 
period, and these in turn are evidence of a greater rainfall 
than the region receives at the present lime. 

The knowledge of such changes is circumstantial, and statistics re- 
garding them are wanting. The cause or causes of such changes, 



CLIMATE AND ITS FACTORS 291 

moreover, are unknown. A change in the inclination of the earth's 
axis would be competent to account for changes in temperature, and 
therefore in rainfall. 

That is, if the axis of the earth were to incline forty degrees, then the 
polar and the tropical circles would have a corresponding distance 
from the poles and from the equator, and the temperate zones each 
would be ten degrees in width, instead of forty-three. Or, if the longi- 
tude of perihelion were to change so that the winters of the northern 
hemisphere should become longer by several days than the summers, 
the ice and snow would collect faster than it would melt, thereby in 
time causing far-reaching changes. 

Changes in the level of a region are also capable of producing varia- 
tions in temperature, and it is highly probable that elevation and de- 
pression have resulted in many of the climatic changes of which there 
is an unwritten record. 

There is evidence to show that the elevation of a region results in a 
lowering of its mean temperature, and the depression of its surface 
has an opposite effect. The surface of New York and the New England 
States was about 1,000 feet higher during the Glacial Epoch than at 
present. 

Zones of Climate. — Zones or belts whose limits are 
bounded by lines of equal average temperature are called 
isothermal zones, and the lines bounding them isothermal 
lines, or isotherms. A comparison of a map of astronomical 
and climatic zones shows that the correspondence of the 
two is only general. The former are fixed and their 
boundary lines are parallels of latitude. The latter change 
their positions with the apparent motion of the sun, be- 
having in this respect like the zones of winds and calms. 
In fact they are all governed by the same law and arise 
from the same cause — the inclination and self-parallelism 
of the earth's axis. 

In the southern hemisphere the temperature is very 
equable, and the isotherms range nearly with the parallels. 
In the northern hemisphere the isotherms are very irregular. 
In which direction do they bend in crossing the great high- 



292 PHYSICAL GEOGRAPHY 

lands of the. earth? In the North Atlantic warm ocean cur- 
rents and their drifts turn the isotherms northward. 

By what isotherms is the climatic torrid zone limited 
north and south? In the spring and the fall its position 
corresponds roughly with that of the astronomical zone. 
The hottest areas are situated not on the equator, however, 
but north of it. In the African desert, Arabia, and the 
arid lands of the United States, the summer temperature 
is above 38° (100° F.) and during unusual hot spells it 
sometimes reaches 49° (120° F.). 

The mean annual temperature of a region reveals but little concerning 
its actual conditions of temperature. These can he studied only from 
monthly isotherms — that is, by comparing the monthly range of tem- 
perature and climate. For this reason, instead of a chart of annual 
isotherms, it is wiser to study two charts, one showing the isotherms for 
midwinter, the other for midsummer. 

The isothermal temperate zones are conveniently limited 
by the lines of 21° (70° F.) and 0° (32° F.). The summer 
limit of the northern zone extends into arctic regions; the 
winter limit on land approximates the fortieth parallel, bul 
on the ocean it is higher. In the Pacific it reaches to the 
sixtieth parallel; in the Atlantic, owing to the drift of the 
Gulf Stream, it penetrates the polar latitudes. 

Extremes of Climate. — The isotherm of highest 
temperature that completely girdles the earth is theoreti- 
cally the thermal equator. Its temperature is probably 
between 27° and 30° (80° to 80° F.). There are several 
isolated regions having a considerably higher temperature, 
however. An extensive region in the Sahara has a mean 
temperature of about 29° (85° F.); in Hindustan and 
South Africa there are other localities equally warm. In 
the American continent an oval-shaped region extending 




ISOTHERMS FOR JULY 




ISOTHERMS FOR JANUARY 



294 PHYSICAL GEOGRAPHY 

southward from the Gulf of California has about the same 
mean. 

The regions of extreme cold are not in the vicinity of 
the geographical pole, but at inland localities considerably 
south of it. In the American continent the area of ex- 
treme cold is near the Arctic Archipelago. In Eurasia it 
is a little to the eastward of the Lena River. In both 
regions the mean temperature is not higher than — 17° 
(0° F.). At Verkhoyansk, Siberia, the temperature 
ranges from - 67° (- 90° F.) to 32° (90° F.). The range, 
one hundred and eighty degrees, is probably greater than 
that of any other inhabited region. 

The highest temperature taken under standard conditions — that is, 
shaded by a double roof with an air space between, and exposed at a 
distance from any radiating surface — seems to have been recorded at 
Warglar, Algeria, where the mercury marked 127° F. In the Colorado 
Desert an unofficial temperature of 136° has been noted. In this case, 
however, it is doubtful if a properly exposed thermometer would have 
registered so much by ten or fifteen degrees. No temperature in this 
region recorded by the Weather Bureau has exceeded 122°, though 
there are several localities, such as Salton Lake and Death Valley, 
where the temperature ranges higher than at any of the Weather 
Bureau stations. The author has repeatedly noted temperatures in 
the Colorado Desert varying from 130° to 145° registered by a thermom- 
eter exposed to the direct rays of the sun. The experience of General 
Greely, U. S. A., Chief Signal Officer, shows the range of human endur- 
ance. At Fort Conger, Lady Franklin Bay, he and his party experienced 
no intolerable discomforts with the temperature as low as — 06°, the same 
officer served in Arizona where the shade temperature was 119° and that 
•of an unprotected thermometer 144°. 

Changes of Season. — Because the earth's axis is in- 
clined to the plane of its orbit, and remains parallel to itself 
while the earth revolves around the sun, it follows that the 
rays of the sun do not fall on a given place always at the 
.same ansrle. 



CLIMATE AND ITS FACTORS 



295 




-s-tws- 



-R-A^-S- 



POSITION OF HEAT-RAYS IN JUNE 



As the earth revolves around the sun, the inclination 
of the axis, together with its self-parallelism, bring each 
temperate zone, in 
turn, to a position 
where the sun's rays 
are vertical. 

The alternation of 
the four seasons is 
realized mainly in 
the temperate zones. 
In the greater part 
of the western coast 
of North America 
the seasons are dis- 
tinguished more by seasonal rains than by variations in 
temperature. Practically there are two seasons — a rainy 
and a dry. Within the greater part of the Torrid Zone 
these are also the chief distinctions of season. In the 

frigid zones the 
distinctions of sum- 
mer and winter are 
also those of day 
and night, each of 
which is six months 
long. 

In general, the 
weather conditions 
of the Torrid Zone 
originate in the east; 
those of the Tem- 
perate Zones in the west. On account of its narrow ex- 
tent, the climate of the southern part of South America 



-s-tws 



— R-A-^-S- 




POSITION OF HEAT-RAYS IN DECEMBER 



296 



PHYSICAL GEOGRAPHY 



is oceanic in character, while most of that part of North 
America in corresponding latitudes is continental. In 
these zones the west coasts are regions of equable; the 
east coasts of extreme climate. Why? 

Deserts. — There are many areas that have little or no 
rainfall. If the rainfall is so deficient that irrigation is 
necessary to produce crops the region is said to be arid; 




ANNUAL MOVEMENT OF THE HEAT-BELT 

if it is too dry for food crops, it is generally considered 
a desert region. 

The term "desert" is also made to include all regions that are 
uninhabitable. 

There is no sharply drawn line between fertile and arid 
lands, or between arid lands and deserts. For instance, 
the Mississippi Basin east of the 2,000-foot contour — pro- 
duces an abundance of food-stuffs. West of this contour 
the climate becomes much drier, and beyond the 2,500- 
foot contour, crops must depend mainly on irrigation. 

In this region turf grass is replaced by scanty bunch 
grass, and beyond the crest of the eastern ranges of the 



CLIMATE AND ITS FACTORS 297 

Rocky Mountains the character of the country in places 
approaches that of a typical desert. In the northern part 
of the Basin Region, the cooler climate and the high 
ridges bring a small amoimt of rain, but in the south almost 
all vegetation disappears and the region is absolutely a 
desert. The same gradation is observed in the great 
African desert. Both north and south of the equatorial 
rain-belt, precipitation decreases little by little; fertile 
lands grade imperceptibly into arid belts, and the latter 
into deserts. 

In the South American deserts the line is pretty sharply 
drawn. The same is true of the" North American desert 
and the Sahara also, if they are approached from the 
western side. 

Only a small part of the various desert areas is desti- 
tute of vegetation, and in such parts the finely pulverized 
rock waste — the "sand" of the desert — shifts hither and 
thither with the winds. In such regions fierce simoons 
and sand-storms prevail. The Colorado Desert, in south- 
eastern California, is an excellent example. 

The climate of desert regions is marked by peculiarities 
and extremes. The winds are hot sand-blasts and whirls; 
the scanty rains come usually in the form of cloud-bursts; 
the temperature is one of intense heat at times alternating 
with bitter cold; the relative humidity of the atmosphere 
rarely exceeds thirty per cent, of saturation. Notwith- 
standing all this, desert climate is wonderfully healthful. 

In popular literature the climate of deserts is supposed to have baneful 
properties, and the expression "poisonous emanations" has a prominent 
place therein. As a matter of fact, desert air is unsurpassed so far as 
salubrity is concerned. It is so free from the germs that produce disease, 
that meat rarely putrefies and food does not ferment. Septicaemia, or 
"blood-poisoning," rarely if ever follows accidental wounds or surgical 



298 PHYSICAL GEOGRAPHY 

operations, and tuberculosis originating in such localities is unknown; 
indeed, desert regions are regarded as the most healthful of all localities 
for consumptives. 

Oases. — A fertile spot in a desert is called an oasis; (he 
latter is fertile because it is supplied with water. For this 
reason the oasis commonly yields a goodly supply of food- 
stuffs. Various causes contribute to the formation of oases. 
The underlying strata may be impervious to water, thereby 
preventing the latter from sinking deep into the soil, 
or there may be a mountain-crest that is sufficiently high 
to condense and precipitate more or less moisture. The 
water flowing down the slopes percolates through the fine 
rock waste at the bottom, much of it being held there in 
suspension. Some of the oases of the North American 
deserts are of this character. 

Geographic Distribution of Deserts. — The distribu- 
tion of deserts constitutes an interesting study. Practically 
two zones, situated mainly between the 20th and 50th 
parallels, north and south, contain nearly all the desert and 
arid lands of the earth. A belt of desert stretches nearly 
across both continents. In North America the belt is 
nearly 1,000 miles east and west. The deserts of the 
Southern Hemisphere are smaller in area only because of the 
smaller land area. In South America it lies tit the eastern 
base of the Andes; in Africa, there is one on each side of the 
Kongo basin. 

"The part of the Sahara destitute of oases has a formidable aspect. 
The path which the feet of the camels have marked out in the immense 
solitude, points in a straight line toward the spot which the caravan 
wishes to reach. Sometimes these faint footmarks are covered with 
wind-blown rock waste, and the travellers are obliged to consult the 
compass, the horizon, a distant sand-hill, a bush, a heap of camels' 
bones, or some other indications which the practised eye of the Tuareg 



CLIMATE AND ITS FACTORS 299 

alone can understand as the means by which the road is recognized. 
Vegetation is rare, and the only plants to be seen are the scrub, con- 
sisting mainly of thorny mimosas; in some sandy deserts there is a 
complete absence of all kinds of vegetation. The only animals to be 
found are scorpions, lizards, vipers, and ants. During the first few 
days of the journey a few indefatigable individuals of the fly tribe 
accompany the caravan, but they are soon killed by the heat; even 
the flea itself will not venture into these dreadful regions. The intense 
radiation of the enormous white or red surface of the desert dazzles the 
eyes; in this blinding light every object appears to be clothed with a 
sombre and preternatural tint. Occasionally the traveller, when sitting 
upon his camel, is seized with a kind of brain fever, which causes him 
to see the most fantastical objects in his delirium. Even those who 
retain the entire possession of their faculties and clearness of vision 
are beset by distant mirages; palm-trees, groups of tents, shady moun- 
tains and sparkling cascades seem to df nee before their eyes in misty 
vapor. When the wind blows hard, the traveller's body is beaten by 
grains of sand which penetrate even through his clothes and prick like 
needles. Stagnant pools or wells, dug with great labor in some hollow 
or other, from the sides of which oozes out a brackish moisture, point 
out each day the end of the stage. But often this unwholesome swamp, 
where they hoped to recruit their energies, is not to be found, and the 
people of the caravan must content themselves with the tainted water 
with which they filled their flasks at the preceding stage. It is said 
that in times of great need travellers have been compelled to kill their 
dromedaries in order to quench their thirst in the nauseous liquid con- 
tained in the stomachs of these animals." — Elisee Reclus. 



Causes of Desert Conditions. — Various causes con- 
tribute to make arid and desert conditions ; but in any case 
a desert is a desert, not because of any natural sterility of 
the soil, but because of the lack of moisture. In some 
localities a high mountain-range that faces the sea winds 
condenses all the moisture they contain and the opposite 
slope with its outlying area is therefore a desert. Thus, 
the Peruvian desert of South America is west of the Andes, 
and the desert of Argentina lies to the east of these ranges. 

In other instances the desert conditions arise from other 



300 PHYSICAL GEOGRAPHY 

and more complex causes. Thus, between the 20th and 
30th parallels there is a downward movement of atmos- 
pheric currents; explain why these may produce deficiency 
or absence of rainfall (p. 225). In some localities the 
winds blowing inland from the sea may enter localities 
"having a temperature higher than that of the winds them- 
selves, and in such instances their moisture is not con- 
densed. The Australian and African deserts result mainly 
from one or the other, or both, of these causes. They are 
unfortunately situated with reference to latitude, and they 
also are lacking in high mountain-ranges. 

QUESTIONS AND EXERCISES.— Referring to any good map, de- 
termine the climate of South America from the following suggestions, 
giving a reason for each statement: What are the conditions of tem- 
perature of the northern part? How do those of the southern part 
differ? In which part is temperature the basis of the seasons? In 
which is rainfall? From which direction do the rains of the northern 
part come? of the southern part? What is the effect of the Andes 
Mountains on the distribution of the rainfall? Give the location of 
the desert and arid regions. Note the effects of altitude on the climate 
of the highlands ; of the lowlands. What evidence does the map give 
to show whether the rainfall of the Amazon basin is profuse or de- 
ficient? Explain why the basin of the Orinoco has two rainy and 
two dry seasons. 

Compare the Asian and American deserts as to origin. How do 
the African deserts compare in this respect? 

Prepare a summary of the climatic conditions of the state or county 
in which you live, noting especially any facts not ordinarily included 
in the general outlines of the subject. From the United States 
Weather Bureau obtain the following: highest temperature observed, 
lowest temperature observed, mean for each month, mean annual 
rainfall, mean for each month, number of rainy days for any year, 
general direction of the winds, other relevant facts. 

From the diagrams, p. 295, find the time at which the sun's rays 
are vertical at the tropic of Cancer. What is the season at this 
time in the Northern Hemisphere? Are the sun's rays direct or 
slanting in the Southern Hemisphere? What is the season there? 



CLIMATE AND ITS FACTORS 301 

What are the seasons when the sun's rays are vertical at the equator? 
On a piece of thin paper trace, with a pencil, the isothermal hot zone 
on the map for January, p. 293 ; cut it out along the lines, and place 
it in its proper position {i.e., for January on the map for July). The 
parts that overlap show the region where summer is continuous all 
the year. Compare this result with the diagram on this page. What 
parts are not covered by the heat-belt? When the heat-belt is far 
north what is the season in the Northern Hemisphere? in the South- 
ern? From the oscillation of the heat-belt show how five zones of 
temperature result. 

COLLATERAL READING AND REFERENCE 

Davis. — Elements of Meteorology. 
Waldo. — Elementary Meteorology. 
Greely. — American Weather. 



CHAPTER XVII 

THE DISPERSAL OF LIFE 

There are two lessons in nature that probably every 
human being of mature years has learned, namely — that 
the earth is full of organisms endowed with that mys- 
terious force called life, and that the life-forms are grouped 
in kinds or species. Moreover, while the individuals of a 
species closely resemble one another, those of different 
species are commonly very unlike. 

Almost every living body or organism passes through 
several stages or conditions. It first appears in the form 
of a germ enclosed in an envelope called an egg, or per- 
haps, a seed. Under the action of heat, or moisture, or 
both heat and moisture, the egg or seed passes through 
various stages of development in which it gradually ap- 
proaches its mature form — the condition that immediately 
precedes death. In general, the egg develops into a life- 
form, known as an animal, the seed into a plant. The egg 
may contain both food and moisture as well within its en- 
velope; but the seed contains food only. The egg very 
easily loses its vitality or life principle; the seed may re- 
tain its vitality for months, or even years. The offspring 
of the egg almost always possesses the power of moving 
from place to place in one or another of its forms of life; 
the offspring of the seed, on the contrary, is rarely ever 
able to move; it spends its life in the spot in which it de- 
veloped into life. 

302 



THE DISPERSAL OF LIFE 



303 



The seed-form of the organism is remarkably adapted 
for transportation and dispersal. Commonly the seeds 
are strong enough to resist no little mechanical force. 
Those of some species will endure a temperature but little 
lower than that of boiling water; they will likewise endure 
the severest cold, and are almost always enclosed in a 




A SNOW-CAPPED BARRIER THAT MANY SPECIES CANNOT PASS 

water-tight case. The egg, on the other hand, will not 
endure extremes of temperature, nor will it survive the 
slightest injury. As a rule, both seeds and eggs float on 
water, and many kinds are carried in the air. 

The stage of growth and development is one of the 
greatest danger to the existence of the organism. During 
this period it quickly and easily succumbs to the most 



304 PHYSICAL GEOGRAPHY 

trifling changes in its surroundings. At this time, too, it is 
apt to be the prey of higher organisms that kill and devour 
it. Indeed, so great is the mortality during the period of 
development that, in many species, not more than one or 
two individuals in many thousand reach the state of 
maturity. 

As the enemies to a species increase, its fecundity is apt also to in- 
crease. Thus, the spawn of a female cod aggregates several million eggs. 
If all these were to hatch and mature, the sea could hold only a few- 
generations of them. 

The mature stage of the organism follows that of de- 
velopment. In this condition it has but one object toward 
which all its energies tend, namely — the reproduction of 
its kind. This accomplished, sooner or later it dies; that 
is, the vital principle leaves it, and it is quickly resolved 
into the mineral elements — the "dust" — which gave it ex- 
ternal form and structure. Man}' species have special 
means for the protection of their bodies; nearly all possess 
special organs for the purpose of nutrition; the higher 
species have organs of locomotion. 

Laws of Structure. — Many laws are concerned in the 
growth, development, and reproduction of organic forms, 
but there are three that govern, directly or indirectly, 
ever}' form of life. These are heredity, nutrition, and 
variation. 

The law by virtue of which the germs of organisms de- 
velop and mature, each into a form of its own kind, is 
called heredity. The germ of a species always reproduces 
forms like those of the parents or ancestors. Acorns always 
produce oak-trees, animals beget of their own kind, and 
the germ that in the human system produces disease, breeds 
nothing but the same disease. 



THE DISPERSAL OF LIFE 305 

Since the discovery of the fact that many diseases are due to the 
growth and development of minute organisms within the human body, 
the science of surgery and that of sanitation have been greatly aided. 
Septicaemia, variously known as "hospital fever" and "blood-poison- 
ing," once the bane of every hospital, is now comparatively rare, and 
such diseases as small-pox, typhoid fever, and cholera may be readily 
quarantined and stamped out. Dirt and filth may be the soil in which 
the germs of these diseases breed, but it does not originate them. 

A seed or an egg develops into an organism that be- 
comes an ancestor of many thousand generations, aggre- 
gating millions of individuals. But in obedience to the 
law of heredity, the individuals of the last generation will 
not differ greatly from their ancestor, nor will they differ 
from one another. 

The process by which food, within the body of an organ- 
ism, is decomposed and then made a part of the structure 
of the organism is called nutrition, or feeding. In obedience 
to this law, new tissue, that is, flesh, blood, bones, etc., 
is constantly being made, and older tissue, no longer use- 
ful, is cast off and destroyed. The number of substances 
required for nutrition is few. Nearly three-quarters of the 
weight of every organic being consists of water; in many 
instances more than ninety per cent, is water. The remain- 
ing part is composed mainly of compounds of carbon, lime, 
nitrogen, hydrogen, and phosphorus. The food must con- 
tain all these substances or the organism will not mature. 
As a rule, plants obtain their food from the mineral king- 
dom, and animals, either directly or indirectly, from plants. 

The law in obedience to which organisms are changed, 
or change themselves, to meet the conditions necessary to 
their existence, is called variation. Thus, under cultiva- 
tion,, the wild rose, no longer needing its multitude of 
stamens, develops them into petals. Under the condi- 



306 PHYSICAL GEOGRAPHY 

tions imposed by its environment, the almond has varied 
its development by taking the form of the peach and the 
nectarine. 

Birds that for long-continued generations have obtained 
their food from the water have become either swimmers or 
waders, and many species that scratch the ground to obtain 
food have gradually lost the power of extended flight. The 
great diversity in the various members of the dog family 
is a familiar example of the effects of variation. The horse 
of present times has but one toe, but the horse of Miocene 
times had three, and of Eocene times four toes on the fore 
feet. The birds of early geological periods were much 
more like reptiles in character than those of present times. 
Some of the reptiles, too, have lost their feet and are 
scarcely a remove from serpents. 

Because of the struggle that has been waging ever since life appeared 
on the earth, only the individuals which can adapt themselves to en- 
vironment are able to survive. Variation is not always a gradual 
change in a whole species; it is quite as often a sudden change in 
individuals; and the transmitted change frequently marks the descend- 
ants. 

Environment. — Variation of species is the result of 
food, temperature, and moisture — that is, the conditions 
of nutrition and environment. These are the conditions 
with which every organism has to battle for existence, 
and these determine all its habits. If the environment of a 
species changes, one of three things is pretty certain to 
take place: the species dies, it migrates, or else it survives 
with changed habits. 

Thus, if in a given locality, the rainfall lessens materially, 
the turfgrass quickly discovers it. In order to obtain the 
necessary moisture, an enormous development of rootlets 



THE DISPERSAL OF LIFE 307 

takes place, and if this development does not procure the 
necessary amount of water, the turfgrass gradually dis- 
appears. If a certain species requires an aggregate of ten 
inches of rain, distributed monthly, it will perish if the 
rainfall decreases to nine inches, or if there is a drought 
of more than thirty consecutive days. It will thrive and 
possibly extend its limits if the annual rainfall increases 
to twelve inches. 

The fruit of the common gooseberry, cultivated in moist 
regions, has a smooth surface; but transplanted to arid 
regions and left to grow wild, the berry finally matures, 
covered with leathery spines. Cultivation, which is only 
another name for change of environment, has resulted in 
all the beautiful varieties of roses; it has produced the 
domesticated fruits from wild fruits; it has made the dif- 
ference between the wild fowl and the domestic fowl of 
the same species. Since the territory inhabited by a 
species is either enlarged or decreased by a change in 
food, temperature, and moisture, and since a change in 
any of these factors sooner or later results in variation, it 
is evident that the distribution and variation of species are 
governed mainly by geographic laws. 

Apparently trivial causes are frequently attended by far-reaching con- 
sequences. For example, the mongoose was introduced into Jamaica in 
order to exterminate the cane-rat, then a menace to the sugar planter. 
The mongoose did not lessen the number of cane-rats, but it exter- 
minated one or two species of ground bird, and with their disappearance 
there came such swarms of cattle-ticks and grass-lice that the existence 
of the cattle herds was threatened. The ground birds had prevented 
any great increase of the insect species; and when the former were 
killed, the latter became an intolerable pest. 

Animals and Plants. — Plants are lower in the scale 
of life than animals. A few species excepted, they have 



308 PHYSICAL GEOGRAPHY 

not the power of voluntary motion, and if they possess 
the power of sensation at all, it is of a very feeble kind. 
They derive their nutrition mainly from the ground and the 
air, being able to transform mineral matter, such as water, 
lime, potash, carbon, etc., into plant tissue. With one or 
two exceptions, plants inhale carbon dioxide and exhale 
oxygen. 

Plants exhibit faculty of intelligence in the feeblest degree 
only. This is observed partly in the way they seek their 
food, and partly by their manner of protecting themselves. 
The roots of a plant will grow in the direction of water, 
and the flower will open with the light and close in dark- 
ness. No species is known that will pursue its prey or 
flee from an enemy. And the reason is obvious: the plant 
does not feed upon other life-forms; it merely transforms 
dead mineral matter into living matter, which is to become 
the food of higher forms. Nevertheless, the plant contains 
a vital force that causes it to live, grow, and reproduce; and 
when this vital force is spent, it dies. 

Animals are far more com} ilex in organization than plants. 
The animal lives by the destruction of other forms of life, 
and therefore it must possess the powers of locomotion, 
prehension, or grasping, and means of defence. All ani- 
mals possess intelligence, and the higher forms have the 
faculty of reason. No exact line of division, however, can 
be drawn between animals and plants. 

Dispersal of Life. — The distribution of life is not a 
matter of chance; on the contrary, it results from the opera- 
tion of fixed laws. Moreover, the question must be ex- 
amined from two sides, namely — the means possessed by 
animals and plants to disperse and, conversely, the barriers 
that operate to prevent dispersal. 



THE DISPERSAL OF LIFE 309 

The means of dispersal are many. All the higher species 
of animals possess the power of voluntary motion. Quad- 
rupeds use their feet; birds fly; nearly all insects have 
at least one stage of development in which they possess 
wings; and fishes swim. Marine currents carry many 
species from the place of their birth to distant parts; and 
still other species are carried by floating matter, and in 
the crops of birds. 

Seeds of plants are carried by the winds, by running 
waters, and in the crops of birds or in the digestive appa- 
ratus of animals. Commerce is responsible for the dis- 
persal of most species used for food and many that are 
baneful to humanity. In short, almost every organism 
possesses means that under ordinary circumstances would 
give it a far wider territory than it now possesses. 

There are many examples of the extension of the habitats of animals 
as a result of commerce. The Norwegian rat in America, the Colorado 
potato-beetle in Europe, and the English sparrow in the United States 
have been spread over a large part of the world in this manner. The 
California species of the phylloxera, a plant-louse infesting the grape- 
vine, was introduced into France and almost destroyed the vines of 
that country. The Russian thistle at one time threatened to overrun 
the wheat-fields of the Mississippi Basin, and the strictest means are 
necessary to keep it under control. The gypsy moth, whose larva? 
infests ripening fruit, has attacked the orchards of the New England 
and Middle Atlantic States, and an expenditure of a million dollars 
a year is necessary to keep its mischievous work in check. The area 
of the cotton-boll weevil has greatly increased. 

The natural or unrestricted migration of species presents 
an interesting aspect. In the temperate zones, as a rule, 
the dispersal has been from west to east; in the torrid 
zone it has generally been in the opposite direction. A 
moment's study will show the reason, namely — the direction 
of atmospheric and marine currents. 



310 PHYSICAL GEOGRAPHY 

Barriers.— But there are region:- in which the species 
carried by marine currents will not thrive, and quite as 
many traversed by winds which sow them with seeds, 
though the soil never fertilizes them. Such extraordinary 
effects cannot exist without causes, and these are the 
natural barriers to distribution. 

The barriers to dispersal are even more potent than its 
agents. These may be reduced to two classes — physio- 
graphic barriers and environment. Chief among the former 
are the high mountain-ranges, oceans and deserts. 

High mountain-ranges form an effective barrier to species 
not provided with means of locomotion; and the more ex- 
tensive the highland the greater the difference of the species 
on the opposite sides. There are two reasons for this. In 
the first place, if animals or plants of a species are unpro- 
vided with means for migration they cannot cross the 
range; in the second place, the conditions of climate on 
the opposite sides of high mountains are so different that 
the species might not survive, even if transported. The 
low temperature of the summit of the range might also be 
fatal. 

The ocean and other wide expanses of water are effective 
barriers to land plants and animals. A few birds endowed 
with unusual powers of flight have crossed the ocean; 
seeds and eggs have also been carried across; and not a few 
species have been transported in vessels. But all these 
are accidental migrations; even then the question of en- 
vironment would still remain. 

Deserts present the same difficulties. Few species are 
able to cross them; fewer still to remain in them, and the 
barrier once surmounted, there may be changed conditions 
which still forbid the existence of the species. 



THE DISPERSAL OF LIFE 



311 



Environment has been considered a cause of variation, 
but it is far more potent as a barrier to the existence of a 
species. If a species requires a temperature higher than 
0° (32° F.), it will perish in a climate having a lower range. 
If it requires an annual rainfall of thirty inches, it will 
perish if the precipitation is materially less; or if it requires 
a monthly distribution of rain, it will not survive any con- 
siderable number of droughts of more than thirty days. 



•■ ^>« > r / '% 










A DESERT BARRIER 

Thus it is seen that every species demands certain con- 
ditions of food, temperature, and moisture. If these are of 
wide range the species will inhabit a wide geographical 
territory; if they are narrow in range, the limits of its ex- 
istence will be correspondingly narrow. If the proportion, 
degree, or quality changes, the species will vary; if en- 
vironment changes materially the species will perish. 



312 



PHYSICAL GEOGRAPHY 



Enemies to Dispersal. — It sometimes occurs, however, 
that a species, once introduced and acclimated, is unable to 
maintain itself, or maintaining itself, is unable to spread to 
any extent over a region whose soil and climate are in every 
way adaptable. There are several reasons for this. The 
region may have been already pre-empted by other species 




THERE MAY BE EXEMTES THAT OPPOSE THE XEW-COMER 



that resist encroachment, or there may be enemies con- 
stantly at work seeking to exterminate the newcomer. 
As a result, there are some species capable of general dis- 
persion that are confined to narrow limits, while others have 
spread themselves broadcast over both continents. 

Thus, turfgrass is easily cultivated, but it has so many 
enemies that in a few localities only does it thrive in a 
wild state. The willow, on the contrary, spreads wherever 



THE DISPERSAL OF LIFE 313 

it is introduced. The ostrich does not extend its territory, 
but the rabbit has become a pest in almost every part of 
the civilized world. 

QUESTIONS AND EXERCISES. — Study the common thistle, the 
dandelion, or the winged maple, and show how these species may be 
spread. 

In the temperate regions of North America in what general direction 
will those species depending on the winds for distribution be most 
apt to spread? 

Note any instance that has come under your personal observation in 
which plants have been carried into new territory by winds, by running 
streams, or by waves. 

Note any instance within your knowledge in which either a natural 
feature or the activity of man has formed a barrier to the dispersion of 
a plant or an animal species. 

What advantages have each of the following species for dispersal? 
the camel, man, the burdock, the ant, the snake, the cotton plant. 

The sting of the tsetse fly, an insect of Africa, is fatal to most cattle $ 
but the offspring of those that survive, are immune from its attacks; 
how will this fact affect the dispersal of cattle? 

COLLATERAL READING AND REFERENCE 
Shaler. — Nature and Man in North America. 



CHAPTER XVIII 

THE GEOGRAPHIC DISTRIBUTION OF PLANTS AND 
ANIMALS 

Probably 150,000 species of plant and about as many 
of animal life are known to exist. These are distributed in 
accordance with the laws noted in the previous chapter - 
that is, each lives in a locality adapted to it. Plant life 
includes species that vary as widely in form and structure 
as the multitude of animal species. 

Plants are grouped in five sub-kingdoms. 

The Prolophytes are the lowest form of vegetable life. Each consists 
of a single cell or of groups of cells. In this sub-kingdom arc included 
the yeast plant, and other similar substances known as ferments, the 
organisms that produce rotting, or putrefaction, and the host of minute 
forms commonly known as "microbes." 

The Thallophytes include the plants in which there is little or no 
distinction between leaf and stem, such as lichens and fungi. Nearly 
all the sea-weeds and the vegetable moulds belong to this sub-kingdom. 

The Bryophytes comprise the mosses and the liverworts. 

The Pteridophytes include the club-mosses, horse-tail rushes, and 
true ferns. All the foregoing sub-kingdoms are flowerless; they re- 
produce by means of minute spores borne in receptacles on some pro- 
tected part of the plant. The dust coming from a bursting puff-ball 
consists of spores, and these have the reproductive properties of seeds 
or eggs. 

The Phanerogams include the species of grasses, shrubs, flowering 
plants and forest trees. Their growth, like that of certain lower forms, 
consists of two parts, the roots and the aerial portion. They reproduce 
by means of flowers and seeds. 

Distribution of Plants. — The distribution or dispersal 
of vegetation may be considered with reference to both 

314 



DISTRIBUTION OF PLANTS AND ANIMALS 315 

abundance and kind. These are best studied as to regional 
position and their altitude. 

The abundance of vegetation is governed mainly by the 
conditions of temperature and moisture. In a climate that 
is both warm and moist, there is nearly always an abun- 
dance of vegetation. Because of this fact, plant life is most 
abundant in tropical lowlands, decreasing as the latitude 
and the altitude increase. In tropical regions it is profuse; 




A FOREST OF THE NORTHERN REGION: OLD GROWTHS AND NEW 

in the temperate zones it is abundant; in cold regions it 
is scanty. 

Two factors, environment and time, seem to control the 
distribution of species as to kind. In the earlier geologi- 
cal ages certain species seem to have prevailed at certain 
centres. From these they have spread in various direc- 
tions. The area over which the species of a region may 



316 PHYSICAL GEOGRAPHY 

have spread is a question chiefly of time; the locality, one 
of environment. The vegetation of a given region is called 
its flora. 

With respect to geographic distribution the map (p. 318) 
shows that the vegetation of the northern regions of the 
two continents does not differ materially. In each con- 
tinent it is a zone of deciduous trees, evergreens, grasses, 
and food-producing plants. Maize, tobacco, the redwoods 
(including the sequoias), and the yuccas are confined t<> 
the American Region. The two regions are separated by 
the Atlantic Ocean, and though the life-forms are not 
always identical, they are very similar. 

The South American Region embraces the territory south 
of the Tropic of Cancer, both mainland and insular. The 
mahogany, cinchona, india-rubber, and rosewood are 
among the chief species peculiar to it. 

The African Region includes Africa south of the Atlas 
Mountains and tropical Arabia. The baobab, oil-palm, 
euphorbias, begonias, the coffee-tree, several heaths, and 
the geranium, are among the native plants peculiar to this 
region. The Oriental Region includes the territory south of 
the Himalaya Mountains, and most of Malaysia. Among 
the principal characteristic species are the spices, (he 
ebony, sandal- wood, and the melons. 

The Australian Region comprises the continent of Aus- 
tralia and most of the islands east and north. The flora 
of this area is peculiar. The prevailing color of the vege- 
tation is bluish-green and the leaves turn their edges to 
the sun. The eucalyptus or gum-trees, the various tree- 
ferns, and the jarrah, a wood much used for street paving, 
are found in this region. In the north and east the Aus- 
tralian and Oriental Regions have many species charartn- 



DISTRIBUTION OF PLANTS AND ANIMALS 317 

istic of both. The eucatyptus and the tree-fern have been 
introduced into California. 

The vertical distribution of species is determined by 
altitude. Thus at the base of the Himalayas and the 
Andes, the flora is tropical; higher up, the characteristic 
species of the temperate zones replace tropical plants; and 
at an altitude of twelve thousand feet, the vegetation is 
that of polar types. 

Most forms of plant life have an important relation to 
mankind, and this is especially true of those used as food, 
as medicine, or in the arts. Chief among them are the 
grains and other grasses, tuberous plants, fruits, those 
yielding textiles, and those used for building timber. Com- 
merce has been the chief factor in the dispersal of these. 

The Grasses and Grains. — The grasses probably ex- 
tend over a wider area than any other family of plants. 
Of these the sugar-cane and maize, or Indian corn, are native 
to the American continent. All the others belong to the 
Old World, but have followed the march of mankind. The 
grasses are the sole food of many species of animals, and 
the seeds are consumed by every race and tribe of mankind. 
The starch they contain gives them their chief value as a 
food-stuff. 

Rice is confined chiefly to the marine marshes and 
moist lands of tropical and sub-tropical regions, but there 
.are several upland species. Rice is the staple food of 
about one-half the people of the world, and is the cereal 
chiefly used in Southern and Eastern Asia. In certain 
parts of China and India, wheat is gradually supplanting 
it. The nutrient value of rice is not quite equal to that of 
wheat. Maize, or Indian corn, a native of the New World, 
is an important food-stuff in temperate and sub-tropical 



DISTRIBUTION OF PLANTS AND ANIMALS 319 

regions. It is the chief bread-stuff of the "mixed" and 
native races of the New World. In the United States and 
Canada it is used mainly as animal food, being converted 
into pork. Its use, both in the form of grain and meat, is 
increasing among the peoples of the Old World. It is also 
used in the manufacture of liquor. 

Wheat is the bread-stuff of the civilized peoples of the 
temperate zones and is the fuel of the activity and energy 
of the world. It is grown in the great plains of the temper- 
ate zones, but it thrives in sub-tropical and sub-polar 
regions. 

The world requires about 2,400,000,000. bushels of wheat 
each year, and the amount required is steadily increasing. 
The annual crop is somewhat greater, but in an occasional 
year the visible surplus falls very low. In 1907 the crop was 
3,000,000,000 bushels. It is estimated that the maximum 
crop possible is about twice this amount. About one-fourth 
of the world's crop is produced in the United States. 

Rye takes the place of wheat in many countries, and is 
one of the most important crops of Russia and Germany. 
A species of oat is native to North America but the culti- 
vated plant is an imported variety. It is a favorite food 
for horses. Barley, about the hardiest of the grains, is 
also much favored as a food for horses, but is employed 
mainly in the manufacture of malt liquors. Buckwheat 
is not a wheat at all; but as it contains a large percentage of 
starch, it is much used as a food-stuff. It is thought to 
have been introduced into Europe by the Saracens, but it 
probably came from Manchuria. 

The canes include the chief sugar-producing plants. 
They thrive best in tropical countries, and are extensively 
cultivated in the sub-tropical belts. In oriental countries 



320 PHYSICAL GEOGRAPHY 

the bamboo, .a species of cane, is much used as a building 
material and in the arts. 

The palms, next to the grasses, probably yield the greatest 
variety of useful products. Cocoa-nuts, dates, sago, sugar, 
wine, and oil, are all derived from this family. So far as 
moisture is concerned, the palms have a wide range, but 
in respect to temperature they are restricted to warm 
regions. They are abundant in both hemispheres. 

Tuberous Plants. — Tuberous plants arc among the im- 
portant food-producers. The potato, probably a native 
of Chile, has been carried to every part of the civilized 
world. It thrives best in temperate latitudes. The yam 
and its relative, the sweet potato, are indigenous to tropical 
America, though a species of the former is found also in 
the East Indies. The beet and the turnip are native to 
Europe. The former is now the principal source of sugar. 
The cultivated onion seems to have come from China, but 
a wild variety occurs in America. The manioc (or manihol ) 
is native to tropical America, but has been transplanted to 
Asia and Africa. 

Fruits. — The fruits are very important, not only as 
delicacies, but as foods. Among the foremost are the fig, 
the date, and the Corinth grape. They are native to the 
basin of the Mediterranean Sea, and the dried fruit is a 
necessary article of food in that region. The Corinth grape, 
an article of no little commercial importance, is sold in 
American markets as "dried currants." 

The cultivated varieties of the apple, pear, peach, and 
plum are native to western Eurasia; the cherry, apricot, 
and almond to the eastern part of that continent. The 
currant is regarded as native to Asia, but wild species are 
certainly indigenous to western North America. The 



DISTRIBUTION OF PLANTS AND ANIMALS 321 

apple and the plum, said to be native to Eurasia, are also 
found wild in North America. The peach seems to have 
originated in Persia, from which the name is derived. 

The melons and their near relatives, the gourds (including 
the pumpkin and squash), are also from Asia. The orange, 
lemon, and lime probably came from the southern slope of 
the Himalaya Mountains. So far as written history is con- 
cerned, the grape has a greater antiquity than any other 
fruit, manna possibly excepted. It is found in a wild 
state in both hemispheres. The fox grape, a wild fruit 
growing in Canada and the New England States, was dis- 
covered and described by the Norse explorers who visited 
North America about a.d. 1000. The cultivated species of 
America are mainly imported; the Concord is an improved 
wild species of American origin. The scuppernong is pe- 
culiar to the South Atlantic States. The cranberry proba- 
bly originated in the temperate zone of North America, 
migrating thence to Europe. The tomato is also native to 
America. 

The banana, which comes to American markets as a fruit 
is more properly a food-stuff because of the large proportion 
of starch it contains. In certain tropical regions, it is 
almost the sole food-stuff. It is estimated that an acre of 
wheat will supply about four or five people with the neces- 
sary amount of grain food; but an acre of bananas will 
support not far from three hundred people. 

Leguminous Plants. — Most of the succulent and le- 
guminous plants, such as the cabbage, lettuce, spinach, 
and peas, have followed the migrations of Europeans. The 
bean seems to have come from Egypt. Celery is un- 
doubtedly of Asian origin, and is found in a wild state over 
a large part of that continent. 



322 PHYSICAL GEOGRAPHY 

Beverage-Yielding Plants. — Beverage-yielding plants 
are cultivated throughout the whole civilized world. Tea 
is sent from eastern and southeastern Asia to almost every 
other country. The best quality is grown on the chain of 
islands east of the mainland; it is also grown. in the United 
States. Coffee, probably a native of Abyssinia, is now 
cultivated mainly in the New World. It grows wild in the 
former region, and a similar species is native to the warm 
parts of California. 

The cacao-tree yields the cocoa of commerce. The seeds, 
dried and browned, are used as an infusion; ground with its 
own fat or with lard it is the chocolate of commerce. 
It is native to tropical America. Mate (mci-lci'), or Para- 
guay tea, is the leaf of a species of holly native to South 
America. 

Spices. — Spices come mainly from Southern Asia and 
the Malaysian archipelago. None except pepper has been 
transplanted to any great distance from its place of nativity. 
Capsicum, or red pepper {chile Colorado), is native to tropical 
America. Nutmeg is a fruit, the covering of which is the 
mace of commerce; cinnamon is the dried inner bark of 
a species of laurel; cassia is a similar species growing 
both in China and the New World; cloves arc the dried 
buds of a tree native to the Molucca Islands and Southern 
India. 

Medicinal Plants. — Medicinal plants are as widely dis- 
persed as is the human race. The opium-poppy, native 
to tropical Asia and possibly to Egypt, has not migrated 
far from the place of its birth. The cinchona, a native 
of South America, but now cultivated in tropical Asia, 
yields quinine and a score of derivatives. The various 
members of the night-shade family yield medicinal sub- 



DISTRIBUTION OF PLANTS AND ANIMALS 323 

stances, among them nux vomica, strychnine, belladonna, 
and gelsemium; they are found in both continents. 

The potato, tomato, and tobacco are the most important American 
representatives of the family. The "jimson" (probably a corruption 
of Jamestown) and other species of the datura stramonium are found 
in all moist and warm regions of North America. 

Rhubarb and ginseng are native to China, but are now 
cultivated chiefly in the United States. The hemp that 
yields cannabis indica, or hasheesh, comes from Southern 
Asia. Coca, from which the drug cocaine is prepared, is 
native to the Andes. Cascara occurs in tropical and sub- 
tropical America. Most medicines widely used are derived 
from plants found in tropical regions. 

Textile Plants. — Plants used in the textile arts have 
followed man in his migrations. Cotton is the furze at- 
tached to the seeds of the cotton plant. Cotton cultiva- 
tion was introduced into America from Hindustan, but the 
Barbados and sea-island species of the plant are native 
to America. Flax and hemp are obtained from the cortex, 
or outer covering of flowering plants; both probably came 
from Africa, but four-fifths of the world's product is now 
grown in the United States. Jute and ramie are native to 
Asia, but are now cultivated in America. More valuable 
than either of these is pita, the fibre of the wild pineapple, 
native to America, and henequen, or "sisal hemp," the 
fibre of the agave. 

Forests. — The forests of the world are distributed with a 
remarkable degree of regularity. The pines and other 
conifers, oaks, elms, maples, willows, chestnuts, and 
beeches, occupy a belt between the 40th and 55th parallels 
that crosses both continents. The distribution of tropical 
forests is not so regular. South America has a flora peculiar 



324 PHYSICAL GEOGRAPHY 

to itself. The palm, mahogany, bamboo, and represental i v< s 
of the pines continue through both continents, however. 

On both sides of the forest belts there are extensive 
treeless areas. Some areas are treeless because they are 
deserts, but in others, such as the plains of Russia and the 
United States, there are few trees because the seeds have 
not been carried thither. The winds that blow over the 
treeless plains of the United States blow from desert re- 
gions; those that sweep the treeless plains of Russia come 
from the ocean and from arid regions. 

In the United States forest trees thrive best in a gravelly- 
soil, but they live and increase in a sedentaiy, prairie soil. 
In the Champlain period that followed the Glacial epoch, 
the northern part of the United States was traversed by 
streams that bore the seeds of various species. Wherever 
the streams deposited gravel they also deposited seeds. 
Hence this region was sooner or later covered with trees. 
As a matter of fact, the timber-covered regions of the 
northern United States are nearly identical with the area 
covered by stream gravel and till. 

Distribution of Animals. — The animal life of a region 
constitutes its fauna. Of the various classes, the mam- 
mals represent the highest types of life, both in form and 
structure and also in intelligence. All the forms of animal 
life possess the attribute of instinct — the hereditary power 
of thought required in the actions necessary to preserve 
and extend life. The higher — perhaps all — forms have 
the powers of reason. These faculties have largely con- 
trolled the distribution of life. 

The animal kingdom is divided into eight great branches or groups; 
these are again divided into classes and subdivided into the following 
orders : 



DISTRIBUTION OF PLANTS AND ANIMALS 325 

Protozoans, the lowest forms of animal life, such as rhizopods, in- 
fusoria. 

Porifera, of which the sponges are the chief species. 

Coelenterates, of which the coral-polyps, jelly-fish, and sea-anemones 
are the best types. 

Echinoderms, represented by the star-fishes, sea-urchins. 

Vermes, or true worms. 

Mollusks, or shell-fish, such as the oysters, clams, limpets, snails, 
and slugs. 

Arthropods, including the types of lobsters, crabs, spiders, scorpions. 

Vertebrates, or animals having the back-bone. 




THE PENGUIN 
A type of Antarctic life. 



The first four species inhabit the water; the remainder include both 
land and water animals. The vertebrates comprise various classes of 
which the principal are mammals, or warm-blooded animals that suckle 
their young; birds, mainly aerial in their habits; reptiles, including 
snakes, lizards, and turtles; batrachians, represented by frogs and toads, 
and fishes. 

The power of locomotion has given a wonderful develop- 
ment to both instinct and reason. These again have been 
controlled by the most powerful motive of animate life, 
namely — the sense of hunger. 

The accompanying map shows certain centres to which 



DISTRIBUTION OF PLANTS AND ANIMALS 327 

animal species are confined. But the limits have been 
determined in a different way from those of plant life. 
The territory of plant flora is governed mainly by environ- 
ment; in animal life environment is important, but the 
power of voluntary locomotion has been the leading factor. 
The limits of a fauna, therefore, are largely determined by 
physiographic barriers. 

The factors that have governed the dispersal of animal species cannot 
always be determined. It must be borne in mind that dispersal began 
in prior geological times, when the conditions of environment were 
often different from those of the present age. In the case of marine life, 
the limits to the territory of species are bounded mainly by the tempera- 
ture of the water. The fauna of cold currents is materially different 
from that of warm waters, and the fact that the lower reptiles of ocean 
waters are uniformly cold, may explain the similarity of Arctic and 
Antarctic marine fauna. Deep-sea species are wholly different from 
surface species. 

In the accompanying map, it is seen that the North 
American and Eurasian regions have a very broad extent, 
and are separated by marine barriers that are neither very 
wide nor impassable. In the south, the regions are sur- 
rounded by barriers that practically isolate them. For 
example, South America is separated from North America 
by the barriers of sea and climate. The African Region has, 
in addition to these barriers, a high mountain range on its 
northern border; the same is true of India; Australia is 
environed by the sea; it is also marked by peculiarities of 
climate. 

The faunas of the two northern regions are similar. In 
many instances the species are identical; in others a spe- 
cies may have its representatives in both continents. The 
faunas of the southern regions, however, are marked by 
strong contrasts. 



328 PHYSICAL GEOGRAPHY 

Northern Regions. — The North American and Eurasian 
Regions have in common many kinds of carnivorous, or 
flesh-eating animals. Various species of wolf and bear are 
widely dispersed through both regions, and the cat family 
is represented by the panther and several species of wildcat. 
Many fur-bearing animals — notably the lynx, otter, ermine, 
badger, and sable — are common to both regions, and so are 
species of the deer family and mountain sheep. 

The grizzly bear, caribou, bison, musk-ox and black 
bear are peculiar to America; the first named is found 
only in the Rocky Mountain highlands. The reindeer, 
camel, buffalo, and nearly all domestic animals are na- 
tive to the Old World, but have been transplanted to the 
American continent. The opossum, puma, bald eagle, 
humming-bird and wild turkey are native to the American 
region; the chamois, ibex, fallow-deer and aurochs are 
peculiar to the Old World. 

South American Life. — The South American Region is 
distinguished by a profusion of animal life. The monkeys 
are unlike those of the Old World. The camel of the Old 
World is here replaced by the alpaca, vicuna, llama, and 
guanaco — all distantly related to the camel, and from which 
the latter probably descended. 

The sloth, armadillo, ant-eater, and peccary arc peculiar 
to this region, and so are the numerous parroquets, and 
hosts of insect species. The condor is the nearest approach 
to the European vulture and the rhea to the ostrich. 

Tropical Regions. — The Ethiopian Region is remarkable 
for the absence of the species common elsewhere. On the 
other hand, the gorilla, lion, zebra, hippopotamus, giraffe, 
ostrich, five-toed elephant and other species arc found 
nowhere else. 



DISTRIBUTION OF PLANTS AND ANIMALS 329 

The Oriental Region is the birthplace of most of the 
domesticated animals. Among wild animals the tiger, 
mongoose, cobra, and three-toed elephant are peculiar to 
this region. The rhinoceros, jackal, and leopard are com- 
mon both here and in the region to the westward. 

Australian Region. — The Australian Region is marked 
by unusual types. All its life-forms are peculiar, and but 




BORN OF THE SOUTH AMERICAN REGION: SURVIVES IN THE OLD 

WORLD 

few types found elsewhere occur in this continent. Many 
species are marsupials — that is, the female has a pouch or 
pocket in which the immature young are carried. Many 
others, such as the kangaroos, have enormously developed 
hinder legs. 

The Bearing of Organic Life upon Physiography. — 
The bearing of life and its energy upon physiographic forms 



330 



PHYSICAL GEOGRAPHY 



is far-reaching and quite as important as the bearing of 
physiographic forces on life. 

Life-forms have been and are now among the important 
agents in rock formation. Some of the limestone basins 
of the Mississippi Valley, all the infusorial earths, the 
various fringing reefs, the barrier reefs, the atolls, and the 




THE KANGAROO 
A type of the Australian region. 



encircling reefs are the work of animal life. The chalk 
formations of Western Europe are also the results of life. 

In the broad areas of the tropical oceans the work of 
organic life is of still greater magnitude. The water of 
these regions is swarming with life, and the skeletons 



DISTRIBUTION OF PLANTS AND ANIMALS 331 

of the dead forms, together with other mineral constitu- 
ents, are accumulating at the bottom. Wherever deep-sea 
dredging has been carried on, these accumulations have 
been found. 

But the secretion of the lime from the sea-water has still 
another effect. After the lime and other mineral matter 
has been absorbed by the organism, the water is specifically 
lighter; as a result, the change in its density has created 
a slow, but certain circulation of water. 

Vegetable life is also responsible for extensive areas of 
rock formation. Under certain conditions, such as exces- 
sive saturation, the leaves, twigs, and stems of plants accu- 
mulate to considerable depths. If these accumulations be 
covered by overflowing sediment, either fluviatile or ma- 
rine, the wood-fibre, after long-continued pressure and par- 
tial decomposition, is converted into coal. 

In the United States coal measures underlie more than 
150,000 square miles of territory, and in the various basins 
of Eurasia a much greater coal area exists. Coal-making 
has been an incident of every geological age. Diamond, 
graphite, anthracite, bituminous coal, mineral pitch, pe- 
troleum, and natural gas are all the results of organic life. 

Vegetation has also been an important factor in pre- 
venting general surface erosion. A surface covered with 
grass or foliage resists the action of rain and winds alike. 
But denuded of vegetation, the surface quickly becomes 
scored by running water; gullies grow into ravines, and 
ravines deepen into impassable canons. 

Not only is vegetation capable of converting a moderately 
dry region into a swamp, but also it may fill the swamp 
and reconvert it into a dry region again. It may accom- 
plish even more than this. A single species, such as the 



332 PHYSICAL GEOGRAPHY 

Russian thistle, may exterminate about every other species 
of plant within the area upon which it intrudes. 

As the native vegetation disappears so do the character- 
istic animals and, sooner or later, the entire flora and 
fauna are changed. This also alters the character of the 
soil; and as the topography of a region is due in part to its 
characteristic vegetation, this also is changed. 

The lowest forms of vegetable life, such as the moulds, 
and the organisms called microbes, perform an important 
office. As disease-germs, they may exterminate whole 
species, both animals and plants. In company with the 
mosses and lichens the}' decompose and crumble the hardest 
rocks. In warm, moist regions exposed rock-cliffs and 
strata are much rarer than in arid regions. Fresh surfaces 
of rock once exposed are quickly covered with mosses, 
lichens, and the various protophytes. These, once es- 
tablished, require time only, either to disintegrate the rock, 
or to cover its surface deep. 

The common earthworm plays an important part. It 
thrives in moist earth, and a colony of these worms, once 
bred in a given locality, continues to inhabit it until rock 
waste is changed to a rich soil. Thus it is seen that the 
lowly and often invisible forms of life become important 
factors in the physiography of a region. 

QUESTIONS AND EXERCISES. — Make a list of the forest trees, 
shrubs, and other wild plants growing in the neighborhood in which 
you live. 

Make a special study of any plant or " weed " regarded as useless or 
baneful. If you cannot obtain the information you require, send a 
specimen to the Department of Agriculture, Washington, D. C. 

Follow the same directions with reference to the animal species, 
especially those injurious to vegetation, applying to the Department 
of Agriculture for information you cannot obtain elsewhere. 



DISTRIBUTION OF PLANTS AND ANIMALS 333 

Enumerate the articles of food and table furniture used at dinner, 
and follow the route of each one from its native place to the table. 

Mention the various uses to which maize or the corn plant is put — 
grain, cob, and stalk. 

In what ways does the wheat crop affect the habitability of the 
United States? 

Name some of the chief causes of the destruction of forests. Note 
an instance in which the cultivation of the cotton plant has affected 
the history of a people. 

Describe instances in which the distribution of animals or of plants 
has been effected by the agency of mankind. 

COLLATERAL READING AND REFERENCE 
Mill. — Realm of Nature, pp. 302-320. 



CHAPTER XIX 

MAN 

Man, though at the head of animate creation so far as 
the development of reasoning powers are concerned, from 
a physiological stand-point is distinctly an animal, and is 
closely related to other vertebrates. The skeleton of a 
man does not differ materially in structure from that of 
a monkey, a bear, a dog, or a bat; it does not differ very 
greatly from that of a whale, a lizard, or a bird ; it closely 
resembles that of the gorilla. 

With respect to nutrition the resemblance is still stronger. 
The digestive apparatus and the various processes by 
which food is converted into blood, bone, and flesh are 
the same in man as in other mammals. The food, more- 
over, is practically the same — water, grain, fruit, and the 
flesh of other animals. The organs by which the blood 
is circulated are the same, and the processes involved in 
breathing do not differ in any essential point in man and 
other mammals. In the structure of bone, muscle, and 
tendon, and in the operation of special organs, such as 
nerves, intestines, lungs, and heart, the functions are prac- 
tically identical. 

The chief characteristic of mankind is the great develop- 
ment of the reasoning faculties. The power of reason is 
certainly common to some of the lower animals— possibly 
to all species. In man, however, this faculty is enormously 
developed in comparison with other animals. Moreover, 

33J 



MAN 



335 



the power of reasoning abstractly seems to be possessed 
by no other species of life. 

The classification of mankind into races and families, 
however, is one of great difficulty and no two ethnographers 
are in full agreement. Color of skin, texture of hair, and 
language have been made bases of classification, but each 
system, closely followed, leads to confusing difficulties. 
The following scheme has 
been tentatively adopted : 

Black peoples. — Negroes, Ban- 
tus, and Negroids (Australians 
and Melanesians) . 

Yellow peoples. — Turanians or 
Mongols, Malays, Turkomans, 
Lapps, Huns and Finns. 

American peoples. — Aboriginal 
or "Indian" tribes. 

White peoples. — The various 
families of the Germanic, Latin, 
and Sclavonic races. 

Black Peoples.— The 

peoples of this type are 
characterized by a black 

skin, kinky or woolly hair, and thick lips. The Negroes 
of Central Africa are the best known of the type. This 
race, native to Central Africa, has been acclimated in 
America, also numbering there about ten or twelve mil- 
lions. The Bantus are the finest specimens of the black 
type, and in their native region are approaching civiliza- 
tion. They are distinguished by a color of skin that is 
bronze rather than black. The features of most Bantu 
tribes are fine and sharp, and the lips thinner than those 
of the Negro. 




THE BLACK TYPE: A SAVAGE 



336 PHYSICAL GEOGRAPHY 

The Australasians inhabit the continent of Australia and 
the near islands. They are tall and slender, have straight 
hair, and represent a very low degree of civilization. The 
Melariesians are native to New Guinea and the chain of 
islands to the southeast. There are also tribes in various 
parts of the Philippine Islands. The Melanesians and Aus- 
tralasians are also called Negroids, or Nigrettoes. Can- 
nibalism is frequently practised among them. 

The black type of mankind is best adapted to a warm 
climate, and the various races are free from the malarial 
fevers and other baneful climatic influences that are so 
fatal to white peoples. In tropical regions the Negro races 
are by far the most enduring peoples. The religion of al- 
most all the people of this type is obeah worship. 

Yellow Peoples. — The yellow or Turanic peoples in- 
habit southeastern Asia. The type is characterized by 
coarse and straight black hair, high cheek-bones, and yel- 
lowish-brown skins. In some, as the Chinese, the eyes 
are set at an angle, giving rise to the term "almond-eyed." 

Chief among yellow peoples are the Chinese, Burmese, 
Anamese, and Siamese. The Caucasians of Transcaucasia, 
who are sometimes taken as a type of the white races, 
belong properly among yellow peoples. The civilization of 
the Chinese is an old one and highly elaborated. In religion 
they are nominally Buddhists, but in fact they are given 
chiefly to ancestor-worship. The Tibetans, among the best 
examples of the race, live in the high and cold plateau of 
Tibet. The Burmese, Anamese, and Siamese live in tropi- 
cal lowlands. The Mongols of western and northern Asia, 
especially the high plateaus, are a race of nomadic horse- 
men, courageous and intelligent. In religion they are .Mo- 
hammedans. Offshoots of the yellow peoples thai have 



MAN 337 

settled in Europe — the Turks, Huns, Lapps, and Finns — 
have reached a high degree of civilization. 

There.have been many invasions of Europe by Mongol peoples. The 
Turks, driven from their home in Central Asia by other Mongols, set- 
tled in the Balkan peninsula in the twelfth and thirteenth centuries. 
The Huns in Europe are connected with an invasion, not of Attila, but 
Balamir, who came from the region northeast of the Caspian Sea, in the 
fourth century. The Lapps and Finns were living on the Arctic Plain 
long before the records of written history begin; they belong to the 
yellow peoples and may or may not be related to the Mongols. 

The Japanese are a mixed race — Mongol and Malay, 
with which Hindu blood probably has been absorbed. The 
Japanese are at the head of the race which they represent, 
and within forty years their civilization and progress has 
put them on a plane with European nations. 

The Malays, or brown race, inhabit southeastern Asia, 
and the islands to the eastward. Most of them are savage, 
but they seem to be capable of an advanced civiliza- 
tion, as is apparent in the Javanese and Hawaiians. The 
Maoris of New Zealand are an excellent type of Malay. 
The Hovas of Madagascar belong to this race. Most of 
the native peoples of the Philippine Islands are Malays. 
The Tagals have reached civilization; the Visayas and Mac- 
cabeles are but little inferior; the Mows are savages. 

American Peoples. — The aboriginal Americans, or 
"Indians," characterized by a brown color, are native to 
the American continent. At the time of the discovery of 
America several tribes, such as the Aztecs and Peruvians, 
were emerging from barbarism into civilization. 

In spite of the free use of red pigments which the Indians were accus- 
tomed to use on their faces, a prevailing characteristic of the race is 
the color of the skin, which inclines to a copper-red. This feature is 
not true of- the Pacific-coast Indians, however, who are distinguished 
by swarthy or black-brown skins. 



338 



PHYSICAL GEOGRAPHY 



Among the pre-historic peoples of the continent none have excited 
more interest than the mound-builders and the cliff-dwellers. Accord- 
ing to popular belief both were a distinct race of people whom the Indians 
exterminated. As a matter of fact, they were nothing more nor less 
than Indians. At the time of the discovery of America by Columbus, 
some of the native Americans were approaching civilization. Most 
of them, however, were still in the stone age, and were therefore in a 
state of barbarism. Still others were in an intermediate state, and 
these had begun to forsake the wickiup, or tepe, for houses constructed 
upon architectural principles. The tribes who had reached this develop- 
ment were responsible for mound-building. The Senecas and Mohawks 




AMERICAN INDIANS 

had already begun to build the famous long houses; the Shawnees, 
Cherokees, and Delawares had not reached quite so high a plane, and 
were still mound-builders. The cliff-dwellers were emerging from barba- 
rism and built their pueblos of selected stone. For better protection they 
commonly built them on high mesas, on cliff-terraces, or even in caves. 
The Zufiis and Moquis are thought to be the nearest living approach to 
the Aztecs. 



In South America and Mexico the Indians have become 
a mixed race, a result of intermarriage with the Latin 
races — especially trie Portuguese and Spanish. In North 
America, on the contrary, where the association between 
Indians and Teutonic peoples has always been marked 
by race hatred, the Indian blood is still pure. 



340 



PHYSICAL GEOGRAPHY 




The Eskimos, one of the most interesting divisions of 
the yellow type, are confined to the American circumpolar 
regions. Thej' are possibly related to the Mongol races, 
but the relation is distant. They seem to be more closely 
connected with such peoples as the Lapps, Finns and 
Samoyacls of the Asian part of the Arctic plain. The Es- 
kimos are short in stature, averaging less than five feet in 

height. They are intel- 
ligent and susceptible to 
civilization. Their habi- 
tations are stone huts; 
their occupation, fishing ; 
their food, raw blubber. 
White Peoples. — 
This race comprises two 
great divisions, each sub- 
divided into various 
families. These divis- 
ions, moreover, repre- 
sent language and rela- 
tionship, rather than 
structure. The color of 
the skin varies from 
light blonde to swarthy, 
closely approximating black among certain peoples. In- 
tellectually, it is the dominating type of mankind. 

The Aryan family is the most widely spread and numer- 
ous of the type. In Asia, it includes the Hindus and 
Persians. In Europe, it includes almost the entire popula- 
tion, the yellow peoples excepted. In the American con- 
tinent, to which its peoples have migrated, it embraces 
about one hundred millions of souls. 



WHITE TYPE 



MAN 



341 



The Romanic family embraces the peoples usually classed as Latins. 
But the Romans were a mixture of Latins, Sabellians, and Etrurians, 
only one element of which is known certainly to be of Aryan descent. 
An infusion of Greek blood developed the fighting powers of the 
mixed race, which led to the conquest of the greater part of Europe. 
When the Western Roman Empire had broken into fragments, the 
Latin language was finally modified by the different races who had 
adopted it, to Spanish, French, Portuguese, and Italian. But the 
Spanish were a mixture of Keltic and Iberian blood, the French were 
of Keltic and Gallic stock, and the Portuguese of Keltic, Gallic, and 
Iberian descent. A certain 
amount of Roman blood was 
intermixed with all these 

peoples, but in hardly an in- <r , „ 

stance is there physically a 
race characteristic among 
them that is distinctively 
Roman. A similar mixture 
took place in the case of the 
English people. Although 
popularly known as Anglo- 
Saxons, the amalgamation is 
far more extensive; it in- 
cludes Angles, Saxons, Jutes, 
and Danes, together with a 
general mixture of Gothic 
blood. To this must also 
be added the infusion of 
Latin blood that came with 
the Norman Conquest, a 
matter of far greater impor- 
tance. 




\\ 



WHITE TYPE: A REPRESENTATIVE OF 
THE HIGHEST CIVILIZATION 



The Teutonic, Latin, Sclavonic, and Keltic branches of 
this family now constitute the most powerful nations in 
the world. They occupy most of Europe and the greater 
part of North America. 

The Semitic family comprises the Hebrews, Moors, Arabs, 
and Abyssinians. The Assyrians and the Phoenicians were 
also of this family, but they have been absorbed, or dis- 



342 



PHYSICAL GEOGRAPHY 



persed by conquest. The Hebrews or Jews hold the chief 
position among Semitic peoples. For about four thousand 
years, in spite of fearful odds against them, they have had 
a commanding position. 

Springing from a family whose native place was not far 
from Syria, the Jews became a nation of considerable im- 
portance. Because of 
steadfastness to their 
faith, neither slavery nor 
conquest has extermi- 
nated them. Diffused 
over the earth, they are 
numerically about as 
strong as ever they were, 
and their religion and 
ceremonial rites are as 
marked to-day as they 
were four thousand 
years ago. 

The Arabs also form 
an interesting ethnic 
group. They occupy 
not only the Arabian 
peninsula, but they have 
extended their habitat 
through the greater part of Africa and much of Central 
Asia. They have but little political organization; on the 
other hand, they are commercial factors of very great power. 
They are the merchants of Western Asia and most of Africa. 
Pygmies. — Scattered over a considerable area of Africa 
are peoples having no ethnographic relation to any of the 
foregoing families. These are the pygmies. So far as the 




A PYGMY 



MAN 



343 



color of the skin is concerned, there are two- classes — one 
having a light brown skin, the other being almost black. 

The existence of pygmy tribes is mentioned by Herodotus, Pomponius 
Mela, Aristotle and others, but as recently as thirty years ago it was 
believed that the accounts of them were mythical. In 1865 the famous 
African traveller, Paul Du Chaillu, discovered the Obongo tribe. His 
accounts were flatly con- 
tradicted in Europe, but 
a few years later they 
were confirmed by Pere 
des Avanchers, an Abys- 
sinian missionary. In 
1871, another tribe, the 
Akka, were discovered 
by Dr. Schweinfurth. 

Of the various 
pygmy tribes the 
best known are the 
Akka, Wambutti, 
and Batua of Cen- 
tral Africa, and the 
Bushmen of the 
southern part. Pyg- 
mies are character- 
ized by a matted 
growth of reddish- 
brown hair upon the 
bodies, prognathic 
jaws and retreating- 
foreheads. The av- 
erage stature of the Bushmen is about five feet; that of the 
other tribes, about four and one-half feet. The Akka are 
characterized by misshapen bodies, long, skinny fingers, 
and withered legs. 




YELLOW TYPE: JAPANESE 



344 PHYSICAL GEOGRAPHY 

Nearly all the pygmy tribes have learned the use of fire, 
but, as a rule, they eat their food raw. Although they 
have a very low place in the human scale, they display con- 
siderable intelligence. The Wambutti are ingenious in 
devising nets and traps for securing game, and they seem 
capable of a low form of civilization. 

The pygmies are rarely at war either with the other 
African tribes or with one another. As a rule, they are 
protected by the tribes. The Obongo pygmies declare 
themselves to be related to the monkeys. The Negroids 
of Australia and the Philippine Islands, and the Hottentots 
of Africa are notably undersized in physical development. 
They have been classed as pygmies, but they have no rela- 
tion to the African pygmies. 

Antiquity of Man. — The written history of man, in- 
cluding that which has been recorded on tablets and monu- 
ments, extends backward only a few thousand years. The 
part of this period recorded in Holy Scripture contains 
data concerning but one or two families and their descend- 
ants. Geological history goes back to a period of greater 
antiquity, but unfortunately gives no clew whereby the 
age of man can be computed in years. Written history did 
not begin until man had reached a comparatively high 
state of civilization, but geological history antedates this 
period, and discovers man living practical]}'' in a wild state, 
as a dweller in caves. 

If man preceded the Glacial epoch, about every trace 
of the species disappeared. If the cave dwellers of the 
Mediterranean or the now famous "Nebraska men," were 
pre-glacial, they certainly were savages. With a few ex- 
ceptions, upon which doubt has been thrown, the oldesl 
traces of mankind are found just above the unsorted drift 



MAN 345 

of the Glacial epoch, and below that of the river gravels of 
Champlain times. Above the glacial drift, however, there 
can be no doubt of the existence of the species. 

It is by no means certain that man did not precede the Glacial epoch. 
A skull found by Professor Whitney among Pliocene deposits and va- 
rious other relics found among the auriferous gravels of California, 
indicates a much greater age than post-glacial existence. As a matter 
of fact, the search for prehistoric and fossil man has been neither ex- 
tended nor systematic. Practically no investigations have been made 
among the Miocene deposits of Central and Southern Asia. 

Both in Europe and America the bones of man, associ- 
ated with those of the cave-dwelling animals he hunted, 
have been found in abundance. With these were also the 
implements of the chase — ornaments, charred pieces of 
bone, and in one instance a rude representation of an 
extinct species of elephant, scratched on ivory. 

This piece is now in the British Museum. Of its origin and antiquity 
there is no doubt. 

From the time of the earliest geological history of the 
species, one feature distinguishes mankind from brute crea- 
tion, namely — rapid intellectual development. Primitive 
man had learned the use of fire, and this in itself was 
to give him supremacy over all other animate nature. He 
had also acquired the use of tools, and these brought a great 
increase of power. The earliest race of people employed 
hammers or axes of rough stone. The next step seems to 
have been the making of polished stone axes, knives, and 
arrow-heads. In western Europe, at one time jade, a 
very hard and fine-grained mineral, supplanted flint as the 
material out of which stone-cutting tools were fashioned. 
The commerce of this mineral opened probably the first 
trade route between Europe and Asia. When, however, 



346 



PHYSICAL GEOGRAPHY 



the primitive man applied fire to the shaping of his tools 
and implements made of metal, his civilization was assured, 
and his power became supreme. 

The metal first employed was a crude alloy now known 
as bronze. At a later period, however, iron was substitu- 
ted for the alloy. Some of these implements were orna- 




EMERGING FROM A SAVAGE STATE 

mental in character, but in the main they were tools and 
weapons. With the increased power afforded by labor- 
saving tools the people who used them emerged gradually 
into civilization. 

Migrations of Mankind. — The history of mankind is 
the history of successive migrations. From the earliest 
times people have associated in families; families have 
grown into clans; and clans into tribes. When a region 



MAN 347 

has been sparsely settled, association and government have 
commonly been patriarchal, the oldest one of the family 
or clan being the leader. 

Where there has been a common enemy, however, the 
plan of association has often been communal as well as 
tribal. The families described in the earlier history as 
recorded in the Old Testament observed a patriarchal 
rule; in later times, the plan of government became com- 
munal and afterward national. The same evolution had 
begun in the history of aboriginal Americans. Families 
had grown into clans and tribes; among Aztecs and Peru- 
vians, tribal association had grown into communal govern- 
ment. 

But there have alwaj^s been limits to the growth of a 
people. They may be absorbed by a stronger race; they 
may be dispossessed and driven to other lands; they may 
be exterminated by enemies; or they may find the region 
overinhabited and incapable of supporting so great a popu- 
lation. For such conditions migration has usually been 
the remedy. 

Thus, tribes of the Tartar race, known in history as 
the Huns, migrated from the plateaus of Asia and over- 
ran a large part of Europe. On their way they drove the 
eastern Goths from their lands, and the latter, in turn, over- 
whelmed Italy and Spain. The Lombards, a Teutonic 
people, migrated from the shores of the Baltic to the Adri- 
atic Sea. The Vandals swept over western Europe, leaving 
behind a trail of fire and blood. They devastated Spain, 
crossed to Africa, and established an empire on the site of 
Carthage. About one hundred years later they were exter- 
minated by a Roman army. Under the teachings of Islam, 
the Arabs devastated the north of Africa, entered Spain 



348 



PHYSICAL G FXX1RAPHY 



and penetrated France. The}' founded a Moorish empire, 
but were afterward driven from Europe. 

The foregoing are but a few of the movements of popu- 
lation that occurred in the short space of three centuries, 
and in the smallest natural division of land. Written 
history takes no note of similar changes that must have 




THE HABITATIONS OF A BARBAROUS PEOPLE 

been going on in other parts of the world at the same time. 
The records of unwritten history, however, furnish many 
instances of the dispersions of peoples that must have taken 
place on a considerably greater scale. In some instances 
the migration was practically a systematic movement thai 
resembled the advance of an army; in other instances it was 
a gradual extension of limits. 



MAN 349 

The migration of the Aryan race is an illustration of 
systematic dispersion. From some part of Eurasia the 
various families of this race wandered westward until they 
occupied all Europe. From Europe, moving still west- 
ward, they have subjugated the American continent, and 
even now the advance guard is knocking at the doors of 
Asia, after nearly completing the circuit of the world. An- 
other branch, the Hindus, migrated southward and settled 
in the plains of the Dekkan. There can be but one explana- 
tion of such a wonderful dispersion. It is the struggle for 
existence — the energy put forth to appease the cravings of 
hunger. 

The Effects of Environment. — Two very remarkable 
factors have tended — the one to change the physical char- 
acteristics of man, the other to preserve them. The former 
is environment, the latter, heredity. The factors of climate 
changed the color of the Aryan's skin from fair to black 
when he took up his abode in Hindustan. Aboriginal 
peoples, such as the Indians of America, the Dravidians 
of southern Asia, the Dyaks of Malaysia, the Ainoes of 
Japan, the Tuscans, Sicilians, and Iberians of southern 
Europe were all dark-skinned people. Their successors, 
in the main, are either white or else approach the white 
type. No doubt the variations in the human species were 
brought about by conditions of soil, food, climate, and 
occupation. It is also certain that, when the variations 
were in existence, heredity made them constant. 

Man's Relation to Physiography. — The influence of 
man as an agent in modifying his environment is often 
overlooked and the far-reaching consequences are not always 
appreciated. These effects may be classified as interference 
with the ordinary course of natural events, in respect to 



350 PHYSICAL GEOGRAPHY 

the surface of the land, to climate, to drainage, and to the 
dispersion. 

The surface of the land has been modified by man in 
many ways. Of these the one of most importance is the 
destruction of forests. In both Europe and the United 
States a very large part of the surface once forest-clad is 
now bare. By various artifices, running streams have been 
made to cover enormous surfaces with fluviatilc deposits, 
and by the same process immense volumes of soil have 
been removed from one place to another. 

Piers and sea-walls have been built so as to extend shores 
to a considerable distance seaward. Thus, nearly one- 
third the area of the Netherlands has been reclaimed from 
the ocean; Venice has become a city of the mainland; and 
considerable areas of New York, Boston, and San Francisco 
are built upon land that has been wrested from the sea by 
the industries of man. 

The various highways, roads, railways, and canals, to- 
gether with the levelling and filling that accompany (he 
growth of cities and towns, form a permanent record of 
mankind. The surface covered by the rubbish carted from 
cities aggregates a large area. It is estimated that the 
surface of Jerusalem has been buried many feet by the 
accumulating rubbish. In places, the city of Rome has 
been filled forty feet deep, and the same result has obtained 
in the vicinity of other cities. 

By drainage, swamps have been changed to dry land and 
their flora entirely replaced by other species. Lakes have 
been drained by canals and ditches, and the lake basins 
given up to cultivation. River basins have been limited 
in area, by jetties and levees, and the area of sediment- 
depositing has been changed from one place to another. 



MAN 351 

Perhaps the most important changes that have resulted 
from the hand of man, however, are connected with the 
dispersal of life. Through his agency various species have 
been transported to all habitable parts of the earth; many 
species have become extinct, and the habits of still others 
have been greatly changed. Only a brief geological period 
is required until the interference of man shall become a most 
important physiographic agent. 

QUESTIONS AND EXERCISES.— Why will not the ordinary laws 
concerning the distribution of life apply to the dispersal of man? 

Make a list, as complete as you can, of the various races and families 
now in the United States ; from what part of the world did each come? 

Name the advantages possessed by man over other species in over- 
coming the restrictions imposed by his environment. In what ways 
can he override such barriers as the sea, deserts, polar regions, and 
regions not habitable by other species? 

How, and in what instances, has the discovery of gold affected the 
migration and dispersal of man? 

Mention one or more instances in which this dispersal has been 
caused by an enemy. 

COLLATERAL READING AND REFERENCE 

Shaler. — Nature and Man in North America. 

Mill. — Realm of Nature, pp. 320-327. 

Marsh. — The Earth as Modified by Human Action. 

Mindeleff. — Migrations of the Cliff Dwellers — Bureau of Ethnology, 

Deniker. — Races of Man, pp. 456-466. 



CHAPTER XX 

THE INDUSTRIAL REGIONS OF THE UNITED STATES 

The main body of the United States extends from the 
colder part of the Temperate ' Zone to the Torrid Zone; 
the isotherm forming the northern boundary of the latter, 
crosses the southern parts of Florida, Texas, and the 
lower part of the basin of the Colorado River. This part of 
the United States is divided na-turally into physiographic 
regions that have fairly well-defined boundaries; and be- 
cause of their features of surface and climate, each region 
has become a great centre of industries that are peculiar to it. 

The boundaries of these regions are both topographic and 
climatic, and the regions themselves differ from one another 
in either climate or topography, or in both. Roughly speak- 
ing, the groups of states commonly recognized do not differ 
very greatly from the industrial groups that result from 
diverse conditions of climate and topography. 

The following are the principal physiographic and in- 
dustrial regions: The New England Plateau, including the 
eastern part of New York; the Middle Atlantic States, 
including the Atlantic Coast Plain and the middle and 
southern Appalachian Highlands; the Great Central Plain, 
including the regions commonly known as the Northern 
States and the Southern States; the Western Highlands, 
including the region west of the 2,000-foot contour, the 
Rocky Mountains, the Columbia Plateau, the Colorado 
Plateau, the Basin, the Sierra Nevada and Cascade Moun- 

352 



354 



PHYSICAL GEOGRAPHY 



tains; and the Pacific Coast Region. Make a list of these, 
grouping each subdivision under its principal division. 

The New England Plateau. — This region embraces 
the northern Appalachian folds, together with areas that 
belong to the Laurentian highlands. During the Glacial 
epoch the Appalachian folds in places were almost ob- 
literated. The Green, White, Adirondack, and Catskill 




THE WATER-POWER HAS BEEN LARGELY SUPPLEMENTED BY STEAM- 
POWER 

Mountains are the principal remnants. Here and there are 
isolated " monadnocks " ; most of these are bosses of volcanic 
rock which were able to withstand the erosion and corrasion 
that resulted during the ice age. Granitic rocks prevail, and 
their rounded surfaces are generally smooth and polished. 

As a result of the Glacial epoch the surface of the New 
England Plateau is very rugged, the only level regions 
being the river flood plains and the old lake basins whose 



INDUSTRIAL REGIONS OF UNITED STATES 355 



waters have disappeared. Many lakes still remain, how- 
ever, and these, a few coast lagoons excepted, are glacial 
lakes, or tarns. Name six of the largest. The slope is 
abrupt and the rivers, therefore, flow iri "reaches"; that is, 
stretches of slack water alternate with rapids and falls. 
The coast is a type of the submerged or "drowned" 




A HARBOR COAST 

region, and the sea now intrudes upon the glaciated regions, 
making the whole shore-line one of coves and fjords. 
Practically all the good harbors of the Atlantic coast of the 
United States are confined to this region and, as a result, 
about four-fifths of the foreign commerce of the country 
goes in and out of its ports. 

The rugged surface consists of uplands and valley lands. 
The uplands are characterized by thin and innutritious soil. 



356 PHYSICAL GEOGRAPHY 

The surface is diversified by drumlihs, eskers, and granite 
hog backs; and much of it is strewn with erratic bowlders. 
The uplands are not capable of supporting a dense popula- 
tion, and in the past half century there has been no material 
progress in agricultural pursuits; on the contrary, fanning 
lands have depreciated in value. As a result there has 
been a constant movement of people from the upland farms 
either to the cities or else to the more fertile regions of the 
west. 

Manufacture has been the chief source of the industrial 
gains. Farming is confined to the lowland valle}'S and re- 
stricted to garden and dairy products. This region is 
celebrated for the manufactures, and these have resulted 
from the abundant water-power. The manufactures form 
a large proportion of the nation's foreign exports. The 
sewing-machines, bicycles, clocks, and firearms made in the 
mills and factories of this region are shipped to almost every 
part of the world; the cotton cloth is used by nearry every 
race of people. 

In the last fifty years the increase of the output of manu- 
factures has been so great that steam has largely supple- 
mented water-power. Some great manufacturing establish- 
ments have been moved to tide water, the cheaper cost of 
coal and transportation being more than an offset for 
water-power. 

The Middle Atlantic States. — This region includes 
the principal part of the Atlantic coast plain, together 
with the middle and southern Appalachians. The lower 
part of the coast plain consists of a belt of swamp kinds 
bordered by sandy pine-barrens. Beyond these there is a 
belt of piedmont lands — the foot-hills of the Appalachian 
Mountains. The rivers flow into estuaries that reach usu- 



INDUSTRIAL REGIONS OF UNITED STATES 357 



ally to the foot-hills and are generally navigable to the 
"Fall Line." 

The soil of this region is not well adapted either to cot- 
ton or wheat, although small quantities of both are grown. 
The chief crops are early fruit and garden stuffs, and these 
find a ready market in the great cities of the manufactur- 




COAL GIVES THE POSSIBILITY OF MAKING STEEL 

Forging a locomotive frame. — Baldwin Locomotive Works. 

ing region. Cotton and tobacco are important crops in 
the southern part of the piedmont lands; and on account 
of the water-power, now tardily developed, the manu- 
facture of cotton textiles is becoming the leading industry. 
The wave-formed spits or barrier beaches are a peculiar 
feature of the coast of this region. Because of them, there 



358 



PHYSICAL C;KO(!RAPHY 



are but few good harbors, and the volume of ocean com- 
merce is therefore small as compared with that of the New- 
England and Middle Atlantic States. How do these bar- 
rier beaches affect commerce? The chief products of these 
beaches and islands is the famous sea island cotton, a 
fibre of long staple and great strength; and this is their 
chief product. The fibre is used in the web of bicycle tires. 




THE CHIEF GRAIN FIELD OF THE WORLD 

The montane part of this section is low and not very 
rugged in the northern, but much higher in the southern 
part. The Appalachian folds contain the most productive 
coal measures of the continent, and for this reason they are 
the seat of extensive iron and steel manufactures. 

In a few instances the iron ore occurs in the vicinity of 
the coal measures, but in most instances cheap transporta- 
tion by water enables the manufacturer to ship the ore 
from the Lake Superior mines tc the smelteries in the 



INDUSTRIAL REGIONS OF UNITED STATES 359 

vicinity of Pittsburg and other points of easy access. In 
some instances the fuel meets the iron ore brought in 
steamers and barges from the Lake Superior iron mines 
to the shores of Lakes Erie and Michigan, and great steel- 
making plants have grown up at Chicago, Cleveland, Lorain, 
Toledo, Ashtabula, and Buffalo. 

From the foregoing it is apparent that the entire Appa- 
lachian region, both folds and plateaus, is an area of manu- 
facture because of certain geographic conditions, and these 
are the existence of power. The waterfall is stored-up 
energy, as also is the coal. The power within the coal 
not only makes the steam that drives machinery, but in 
the smelting furnace it also separates the iron from the 
ore; and inasmuch as iron and steel form the basis of most 
manufactures, the existence of coal implies the develop- 
ment of a great centre of manufacture. The steel rails 
made in these great plants are shipped to various parts of 
the world. The rails and bridges of the railway across 
Siberia were made of Lake Superior ore, mainly in the vi- 
cinity of Pittsburg. 

The Great Central Plain. — From Hudson Bay to the 
Gulf of Mexico the Great Central Plain is characterized by 
a level or a gently rolling surface, sloping toward the 
Mississippi River — the whole declining gently from the 
Heights of the Land, to Hudson Bay on the north and 
the Gulf of Mexico on the south. 

Most of the rivers flow in channels that are from one 
hundred to three hundred feet lower than the general level 
of the land, and their high banks are the bluffs of this re- 
gion. For the greater part, the bluffs are from two to ten 
miles apart, and there is a very level flood-plain between 
them — the famous "bottom lands." All through the 



360 



PHYSICAL GEOGRAPHY 



Great Central Plain the soil is naturally very fertile; that 
of the bottom lands is especially productive. 

The level surface and the general conditions of topog- 
raphy make this region one of sameness so far as external 
appearance is concerned. Climatic conditions, however, 
make two separate and distinct areas of history and indus- 
try; therefore it is divided into Northern states and Southern 
states. The two groups are roughly separated by a bound- 




A MODERN HARVESTER 
It could not be used in a rugged country. 



ary which practically separates the cotton region from that 
of food production and manufacture. 

In the Northern states wheat, corn, oats, and grass have 
always been the chief products. Because of the level sur- 
face and the deep, nutritious soil the grain crops can be 
both planted and harvested at the minimum of expense. 
Under no other conditions of topography could there have 



INDUSTRIAL REGIONS OF UNITED STATES 361 

been such a wonderful development of planting and har- 
vesting machinery. As a result, this region has become 
one of the principal food-producing regions of the world. 
It produces one-fourth of the world's crop of wheat, a con- 
siderable proportion of the dairy products, and about three- 
fourths of the corn. Moreover, the productiveness of the 
land is due very largely to the character of the glacial drift 
spread over the surface. 

The western part of this region — the part beyond the 
2,000-foot contour — does not receive an amount of rain 
sufficient to mature grain; but bunch grass and alfalfa, a 
species resembling clover, are the food of great herds of 
cattle. As a result, the Northern states produce the flour 
and meat not only for the United States, but much of that 
required by the rest of the world. 

The Southern states produce about four-fifths of the 
world's supply of cotton. Grain can be grown in these 
states, but the crop does not pay nearly so well as cotton; 
and cotton cannot be grown north of the line that separates 
the two groups. The industries and social conditions — 
and, therefore, the history — of the two sections have dif- 
fered greatly. 

There has always been much manufacture in both sec- 
tions, but the manufactured articles have been closely re- 
lated to the grain and the meat product in the one section, 
and to cotton-growing in the other. These manufactures, 
moreover, have been greatly encouraged by the extensive 
coal measures mainly in the northern section. Most of the 
cotton is shipped abroad, to be made into textiles else- 
where. Steel manufacture has also become a great in- 
dustry in the southern Appalachian region. 

The Western Highlands. — The Western Highlands em- 



362 



PHYSICAL GEOGRAPHY 



brace the region between the Rocky and Sierra Nevada 
This region is characterized bv rugsedness. The 



Ranges. 



lofty ranges that form the rims of the highland are less 
than two miles in altitude in few places only. Fremont 
and South Passes are the chief channels of intercommunica- 
tion on the eastern side. One of the Pacific railways en >ss< is 




Lfffe4^£kl 



HAGERMANS PASS 
The ranges and canons arc a barrier to intercommunication, 

these ranges at an altitude of nearly 10,000 feet. Tn the 
north the canons of Columbia River and its tributaries 
afford the grades for railway communication; on the south 
the river canons and passes are also the routes of commerce. 
The ranges of the Rocky Mountains are lofty folds rest- 
ing on granitic rocks. The Sierra Nevada and Cascade 



INDUSTRIAL REGIONS OF UNITED STATES 363 

Ranges are huge blocks of tilted rock with a gentle slope 
on the west and an abrupt escarpment on the east. The 
parallel ridges of Nevada, commonly called the "Basin 
Ranges," are excellent examples of block mountains, the 
upturned edge of the block constituting the range. Here 
and there are the isolated knolls that form the laccolites of 
which the Henry Mountains are examples. 

The western slopes of the Sierra Nevada and Cascade 
Ranges receive a generous rainfall. Within the rim ranges 
the rainfall is deficient. In the northern part it is sufficient 
for a rather scanty pasturage, but the southern part is a 
desert. 

The Columbia Plateau, or " Plains of the Columbia," is 
mainly the surface of the great flood of lava that flowed 
from fissures on the Sierra Nevada Mountains. The gen- 
eral surface of the plateau, the block ranges excepted, is 
level, but the region has been much dissected by the rivers, 
whose canons are from five hundred to more than three 
thousand feet deep. 

In several places the Columbia River has cut its channel deep into the 
flood of lava. In one place there is disclosed a forest which was over- 
whelmed by the lava. The trees are felled, but the wood is in a good 
state of preservation. Coulees of lava flowing across the river channel 
have created rapids and falls at various places. 

The Colorado Plateaus, sometimes called the "Alcove 
Lands," consist of a series of table-lands varying from half 
a mile to a mile and a half in altitude. The lower plateaus 
are desert regions of tropical temperature, inhabited by 
a few tribes of squalid Indians. The middle plateaus 
have sufficient rain for a very scanty covering of grass ; 
the higher mesas have a moderate growth of grass and 
timber. 



364 PHYSICAL GEOGRAPHY 

Canons with angular outlines and steep walls are the 
chief characteristic, of this region. The canons of the 
Colorado, which have made the region famous, in places 
are more than a mile deep. Probably nowhere else on the 
face of the earth are the features of erosion and corrasion 
presented on such a stupendous scale. Every river and 
every tributary is practically an underground stream, so 
deep are their channels cut into the plateaus. 

The Basin Region receives its name from the fact thai 
none of its drainage reaches the sea. On the slopes of the 
block ranges the rivers are vigorous streams, but their 
waters finally disappear by evaporation, and by percolation 
in the sea of fine rock waste at their bases. 

At times the beds of some of the larger streams, such as Humboldt 
and Carson Rivers, are dry in the day but contain a considerable amount 
of water at night, when, by reason of lower temperature, evaporation 
is lessened. 

The lakes are without outlet to the sea, and most of them 
are the shrunken remnants of two great lakes that once 
covered a large part of this region. One of these, now- 
called La Hontan, included the present basins of Hum- 
boldt, Pyramid, Winnemucca, and several other lakes ad- 
jacent. Several of them, including Walker and Owens 
Lakes, have never wholly disappeared and their waters are 
saturated brines. 

Great Salt, Utah, Sevier, and Parowan Lakes are the 
remnants of former Lake Booneville (p. 181). Of the 
various remnants many have wholly disappeared, and 
Sevier and Parowan Lakes are now dry; Utah Lake is 
fresh. Great Salt Lake at present is shrinking rapidly. 
Pyramid, Carson, and Winnemucca Lakes, in recent times 
dry, are now filling. 



INDUSTRIAL REGIONS OF UNITED STATES 365 

Two small areas of the Basin Region are below sea-level. 
One of these, Salton Lake and its basin, nearly three 
hundred feet below sea-level, was undoubtedly the former 
head of the Gulf of California; the other, Death Valley, may 
have been. The "sink" or dry bed of Salton Lake, once 
known as Coahuilla Valley, or the Sink of San Felipe, was 
most likely separated from the present Gulf by the sedi- 
ments brought down by the Colorado River. This region 
is now called Imperial Valley, and much of it has been made 
cultivable by irrigation. The sediments formed a bar or 
sea wall across the Gulf and cut it in twain. The upper 
portion in places has become partly filled with wind-blown 
rock waste, but its lowest part is about three hundred feet 
below sea-level. 

Several of the sinks of this region are fed, not by rivers 
that normally flow into them, but by the overflows of the 
Colorado River. When more than bank-full, the latter 
overflows into the lower land to the westward. Salton 
Lake is an overflow of this character. New and Hardy's 
Rivers, frequently chartered on maps of this region, are 
not streams flowing into the Colorado, but out of it. In 
this locality the river practically flows around the side of a 
slope; and at times, when the volume of water is too great 
to be contained in the channel, the water breaks its con- 
fining bank and temporarily flows out into the desert. 

At the time of the filling of the basin in 1891, the water was extremely 
salt, and its temperature was nearly 120° F. At several times there 
have been propositions to turn the river into the sink and thus make 
an inland sea. Evaporation is so great, however, that the entire 
volume of the Colorado would fill but a small part of the basin. 

The climate of the Basin is one of great extremes, and 
the southern part is one of intense summer heat. In places 



366 



PHYSICAL GEOGRAPHY 



it is a region of dunes swept by simoons, and occasionally 
deluged by cloud-bursts. To the latter arc mainly due the 
■ sinks and washes of the region. Yuccas, cacti, mezquit 
(a species of acacia), and a coarse grass resembling the 
spinifex of Australia, are the prevailing vegetation of the 
southern part; sage-brush, a kind of wormwood, is char- 
acteristic of the northern region. Wherever irrigation is 
possible the soil of the river flood plains is highly pro- 




MOUNT RAINIER 
It is the cinder-cone o] an extinct volcano. 



ductive. In the southern part several species of lizard, 
among them the "horned toad," abound. A large species, 
popularly known as the "Gila monster," inhabits the Gila 
River and is peculiar to this river valley. 

The conditions of both climate and topography will not 
permit the Western Highlands to become a thickly peopled 
region. The rainfall is insufficient for the production of 
any great amount of food-stuffs, and the latter must de- 



INDUSTRIAL REGIONS OF UNITED STATES 367 

pend upon irrigation wherever they are grown. The rug- 
ged surface is intensified by deep canons, and these are 
such obstacles that commerce is carried on at an enormous 
expense. In one or two instances a canon half a mile in 
width forces traffic to make a detour of several hundred 
miles around. The mining of the precious metals, copper, 
and lead, is the chief industry. 

The Pacific Coast Region. — This region includes the 
western foot-hills of the Sierra Nevada and Cascade Ranges, 
the Coast Ranges, and the great intermontane valley be- 
tween them. A notable feature of this region is the dis- 
tribution of rain. During the winter months the moist 
westerly winds are sufficiently chilled and shed an abun- 
dance of rain over almost the entire region; very little falls 
from May to October, and in southern California, none at all. 

The foot-hill region is more or less rugged, but the 
greater part of its area forms excellent ranges for cattle 
in the north, sheep in the south, and fruit in every part. 
The Coast Ranges lie abruptly against the shores of the 
Pacific Ocean and in only a few places is there even a 
narrow coast plain. The few harbors, however, are deep, 
commodious, and conveniently situated. In a few places, 
however, vessels lie alongside a high cliff and receive their 
cargoes by means of chutes with long outriggers. The 
lower ranges of these mountains form excellent pasturage; 
the river valleys produce the best wheat that is grown. 

The great intermontane valley is a rift that extends from 
Puget Sound to the Gulf of California. It varies from 
twenty to about one hundred and fifty miles in width, but 
in several places it is interrupted by cross spurs that connect 
the great ranges. In the north, where it opens to the sea, 
it is known as the Sound Valley. Farther south the Golden 



368 PHYSICAL GEOGRAPHY 

Gate opens from the sea into San Francisco Bay, one of the 
principal harbors of the world. This part of the inter- 
montane region is best known as the Sacramento-San Joa- 
quin Valley. Between them is the Willamette Valley. 

The northern and southern parts of the intermontane 
valley form a mammoth wheat field; the middle portion 
consists of rolling lands that form excellent cattle and 
sheep ranges, and furnish the possibilities of unlimited 
water-power not yet utilized. South of Tehachapi Pass, a 
fertile lowland lies next the Pacific, which yields an abun- 
dance of semi-tropical fruits and a very fine merino wool. 
The conditions of climate and topography make this region 
capable of supporting an enormous population. 

The Adjustment of Industrial Pursuits to Environ- 
ment. — In the growth and development of a nation two 
processes usually are going on — the acquisition of territory 
and the adjustment of the pursuits of a people to the condi- 
tions of their geographic surroundings. The latter is usu- 
ally attended with more or less friction, and the friction 
is a very large factor in their history. 

In the geographic distribution of the industries of the 
United States, one may follow the processes of adjustment. 
The New England Plateau, with its abundant water-power 
— helped also by steam-power — furnishes the country with 
light manufactures and textiles and exports the balance. 
The people of the harbor region carry on the foreign com- 
merce and largely control the great railway systems 
that transport the manufacturer's products and the 
food-stuffs. 

The people of the Appalachian region manage the distri- 
bution of the coal and supply the country with steel rails, 
bridge material, building girders, and power-producing ma- 



370 PHYSICAL GEOGRAPHY 

chinery. From the prairies of the Great Central Plain 
come the breadstuff's and meat, and from the Atlantic 
Coast Plain the fruit and vegetables required for the labor- 
ers in the crowded manufacturing centres. From the south 
conies the cotton and from the west the wool that is to 
clothe eighty millions of people. From the Western High- 
lands are obtained the gold and silver, the medium of com- 
mercial exchange, and much of the copper the medium by 
which electric-power is transmitted. Each section sup- 
plies not only the rest of the United States, but a large 
foreign trade as well. 

Natural Resources. — No other nation, China excepted, 
possesses such a great wealth of resources. Sonic of these 
will still last for years, but others are nearly exhausted. 
The bison and the fur-seal are practically extinct, the former 
being in part replaced by cattle that certainly are of greater 
value. 

The most valuable forest trees of the country are the 
pines. Of these, a belt of white pine extends along the 
northern border; and a belt of yellow pine along the At- 
lantic and Gulf coasts. Both of these regions are nearly 
exhausted of their supply of merchantable timber. The 
dense forests of Douglas fir, or "Oregon pine," and red- 
wood of the Pacific Coast will be productive for a much 
greater length of time. The amount of growing timber is 
probably greater than at any previous time in the history of 
the country, but very little of it is fit for building purposes. 
It is estimated that from five to ten million young pines are 
destroyed each year for use as Christmas trees. 

Forest fires probably rank first in the destruction of timber. The 
railways make the heaviest demand on the oak, which is used for tics. 
The paper-makers use an enormous amount in the manufacture of 



INDUSTRIAL REGIONS OF UNITED STATES 371 

paper pulp; the charcoal burners destroy the rest. Between the rail- 
ways and the tanneries the Pennsylvania Appalachians are nearly shorn 
of oak and hemlock. 

The coal fields cover an area of about 130,000 square 
miles. Of the amount yielded from these mines, all the 
anthracite coal comes from three small areas in Pennsyl- 
vania; these, it is estimated, will be exhausted in about 
one hundred years. There are now known to be anthracite 
fields of considerable extent in Colorado, however. The 
supply of bituminous coal is practically unlimited. Much 
of the coal supply is used as house fuel, but by far the 
greater part is used in the manufacture of iron and in pro- 
ducing steam. 

Most of the coal occurs in the rocks of the Carboniferous 
Age; the coal measures of the Pacific Coast, however, are 
of much more recent origin, and formed during the Tertiary 
period. 

Petroleum, or rock oil, occurs in various places, usually 
near but not always in the coal fields. The refined oil of 
commerce is shipped to almost every part of the world, 
and is even an article of caravan trade in Africa. The 
principal wells of the United States are in Western Penn- 
sylvania, Eastern Ohio, West Virginia, and Texas. There 
is also a productive region in Southern California. Natural 
gas occurs in the same general area, but the gas and the oil 
do not seem to be associated. The gas is used for house 
fuel and for making steam. The supply, much of which 
has been wasted, is becoming exhausted. 

Iron ore occurs in very many parts of the United States, 
but it is available onfy when it can be shipped to places 
where coal is cheaply obtained. The ores of Lake Superior, 
Iron Mountain in Missouri, and the Appalachian Mountains 



372 PHYSICAL GEOGRAPHY 

are the chief supplies. The iron is obtained from the ore by 
smelting the latter with coal or coke, and is then converted 
into steel ingots. The ingots are rolled into rails, plates, 
billets, and other structural material. 

Gold is abundant in the Western Highlands. It is 
obtained mainly by crushing the quartz rock in which it 
occurs and amalgamating, or dissolving the gold in quick- 
silver, or by the use of other solvents. In Alaska and 
in parts of California most of the gold is free, being 
mingled with gravel. It is obtained by washing the lat- 
ter away with water, thereby leaving the gold, which is 
much heavier, to be taken up by the quicksilver. Silver 
also occurs in the Western Highlands. Copper occurs in 
the Rocky Mountains, but the principal part of the prod- 
uct comes from the Lake Superior region. It is mainly 
used for the transmission of electric power. One of the 
two great quicksilver-producing regions of the world is in 
California and this state yields about half the output. 

QUESTIONS AND EXERCISES. — Repeat the list of physiographic 
and industrial regions enumerated in the first page of this chapter. 

Why is the New England Plateau ill-adapted to grain-farming? 
How does topography become a factor in the economic production of 
grain? 

State the various ways in which coal is used as power, both on 
land and at sea. 

Study the furniture and equipments of the schoolroom and make 
a list of the industries there represented. Trace the geographic 
source of the raw material employed; where is each manufactured? 

Explain how the topography of the northern prairies has affected 
the development of farming machinery. 

Explain why cotton-growing is limited to its present latitude. In 
what way has cotton-growing affected the social conditions of the 
people of the Southern States? 

Explain how and why the topography of the Western Highlands is a 
barrier to commerce. 



INDUSTRIAL REGIONS OF UNITED STATES 373 

Explain how and why the geographic distribution of industries has 
resulted in the enormous development of railways. 

Describe three railway routes across the continent; two water 
routes from Chicago to tide water. 

How does the grade of a railway affect the cost of transporting 
freight? 

Obtain from the Hydrographic Office, Washington, D. C, any 
bulletin or publication explaining the kinds and uses of buoys and 
range lights employed in harbors. 

Trace the course of a deep draught steamship entering the main 
channel of New York Harbor, with reference to the range lights. 
(See map, p. 353.) 

COLLATERAL READING AND REFERENCE 

Powell. — Physiography of the United States, pp. 33-100. 

Davis. — Physiography of the United States, pp. 269-304. 

McGee. — The Piedmont Plateau, National Geographic Magazine, 
vii., 261. 

Hewes. — Statistical Railway Studies, American Railways, pp. 425- 
449. 



APPENDIX 



The Elements of the Solar System 



Name. 


Distance from 
Sun, in Miles. 2 


Time of 
Revolution. 


Diameter 
in Miles. 


Number 
of Satel- 
lites. 


Density 

Water 

= 1. 


Sun 






860,000 

2,992 

7,660 

7,918 

4,211 

20—300 

86,000 

70.500 

31,700 2 

34,500 2 


1 
2 


1 4 


Mercury 

Venus 

Earth 

Mars 

Asteroids. . . . 


37,750,000 

66,750,000 

92,300,000 

141,000,000 

250,000,000 

480,000,000 

881,000,000 

1,771,000,000 

2,775,000,000 


88 days 

224 " 

365i " 

1 . 9 yrs. 

4.4 1 " 

11.8 " 

29.5 " 

84 ". 

164 " 


6.8 2 
4.8 2 
5.6 
4.2 


Jupiter 

Saturn 

Uranus 

Neptune 


5 
8 
4 
1 


1.4 
0.7 
1.3 2 
1.1' 



1 The periodic time of the asteroids varies from 3.1 years to 7.8 years; the approx- 
imate average is 4.4 years. 

2 These values are approximate. 



II 



Deep Borings 



The following list of borings represents depths existing 
in 1905. It is subject to change: 

Feet. 

Paruschowitz, Upper Silesia 6,570 

Schladebach, near Leipsic 6,265 

Monongahela (thus far sunk) 5,532 

Wheeling, W. Va 4,920 

375 



376 APPENDIX 

Feet. 

Sperenberg (gypsum beds near Berlin) 4,559 

Lieth, near Altona 4,388 

Eu, near Stassfurt 4,2 1 1 

Lubtheen, in Mecklenburg 3,9 19 

St. Louis, Mo 3,843 

Stennewitz, near Halle 3, 04 4 

Inowrazlaw, Posen 3,024 

Friedrichsaue, near Aschersleben 3,542 

There is but little uniformity, however, in the rate at 
which the heat increases; it varies from one degree (F.) in 
fifty to one in every seventy or eight}' feet of descent. 
In some cases the heat is due in part to chemical changes in 
the rock. 



Ill 



Heights of Plateaus, Ranges, and Peaks 



Plateaus 



Feet. 

Abyssinian 0,500— 7,500 

Allegheny 1,000— 1,500 

Australian 4,500— 5,500 

Bolivian 12,000—14,000 

Brazilian . 2,500— 2.800 

Colorado 4,500— 0,000 

Columbia 4,000— 5,000 

Dekkan 2,000— 2,500 

Guiana 2,000— 3,000 



Feet. 



Heights of the Land 1,000— 1,500 

Iberian 2,000— 2,500 

Iran 5,000— 0,000 

Mexican 7,000— 8,000 

Mongolian 3,000— 4,000 

New England 1,000— 1,200 

The "Plains" 5,000— 0,000 

The Pamirs 10,000—14,000 

Tibet 15,000—17,000 



Ranges 



Alps 

Altai 0, 

Andes 12, 

Apennines 3, 

Appalachian 1 

Atlas 8 

Balkan 4 

Blue (Oregon) 4, 

Carpathian 4, 

Cascade 7, 

Caucasus 9, 

Coast (California).. 2, 



Feet. 
000— 9,000 
000— 7,000 
000—15,000 
500— 4,000 
500— 2,500 
000—10,000 
000— 5,000 
000— 4,500 
500— 0,000 
500—10,000 
000—1 1 ,000 
500— 3,500 



Feet. 

Coast (Canada).. . . 4,500— 8,000 
Dragon (So. Africa) 4,000— 5,000 

Himalaya 10,000—19,000 

Hindu Kush 10,000—18,0(10 

Jura 2,500— 3,500 

Karakorum 18,000— 19,000 

Ozark 1,200— 1,500 

Pyrenees 7,500— 9,000 

Rocky (U. S.) 0,000— 7.000 

Rocky (Canada). . . 9,000—10,000 

TianShan 17,000— is, odd 

Ural 2,000— 4,000 



APPENDIX 



377 



Peaks 



Feet. 

Aconcagua 23,900 

Ararat 17,260 

Blanc 15,744 

Ben Nevis 4,368 

Chimborazo (volcano) 20,500 

Cotopaxi (volcano) 16,300 

Dapsang 28,300 

Demavend (volcano) 18,800 

Etna (volcano) 10,875 

Elbruz 18,526 

Everest 29,000 

Fremont Peak 13,790 

Fujiyama (volcano) 14,177 

Hekla (volcano) 5,100 

Hood 11,900 

Kenia 18,000 

Kilima Njaro 20,000 

Kilauea (volcano), Ha- 
waiian Islands 4,000 

Logan 19,500 



Feet. 

Marcy, New York 5,467 

McKinley, Alaska 20,464 

Mauna Kea (volcano), 

Hawaiian Islands 14,000 

Mauna Loa (volcano) 13,600 

Mitchell, North Carolina. . 6,711 
Hooker, British Columbia . 15,700 

Orizaba (volcano) 18,300 

Pike's Peak 14,147 

Popocatepetl (volcano) . . . 17,800 

Rainier (Tacoma) 14,441 

St. Elias 18,024 

Shasta 14,440 

Sinai 8,600 

Teneriffe 12,000 

Washington 6,286 

Whitney 14,898 

Vesuvius (volcano) 4,000 

Wrangell 17,500 



IV 

Lengths of Rivers and Areas of their Basins 1 



Miles. 

Amazon 4,000 

Amur 2,500 

Brahmaputra 2,000 

Colorado 1,100 

Columbia 1,400 

Danube 1,800 

Dnieper 1,230 

Dwina 700 

Elbe 550 

Ganges 1,800 

Hoang 2,800 

Hudson 300 

Indus 2,000 

Irawaddi 1,200 

Kongo 3,000 

La Plata 2,300 

Lena 2,800 

Mackenzie 2,400 

Mekong 2,600 

Mississippi-Missouri4,200 



Sq. Miles. 

2,500,000 
750,000 
400,000 
230,000 
290,000 
300,000 
200,000 
150,000 
450,000 
450,000 
400,000 
13,000 
350,000 



1,500,000 

1,250,000 

750,000 

600,000 

300,000 

1,250,000 



Miles. 

Murray-Darling 1,100 

Niger 3,000 

Nile 4,000 

Ob 2,800 

Orange 1,200 

Orinoco 1,500 

Po 450 

Rhine 800 

Rhone 550 

Rio Grande 1,800 

St. Lawrence 2,100 

Sao Francisco 1,800 

Seine 500 

Thames 215 

Tocantins 1,000 

Volga 2,300 

Yangtze 3,100 

Yenesei 3,000 

Yukon 2,200 

Zambesi 1,800 



Sq. Miles. 

350,000 

1,000,000 

1,250,000 

1,000,000 

275,000 

400,000 

27,000 

90,000 

35,000 

200,000 

560,000 

200,000 

23,000 

6,000 

250,000 

600,000 

700,000 

1,500,000 

400,000 

500,000 



1 Both the length and the area of the basin are approximate. 



378 



APPENDIX 



V 

Lakes 



Name. 



Aral 

Assal 

Baikal 

Balkash 

Caspian 

Chad 

Chapala 

Crater 

Dead Sea .... 

Erie 

Great Salt. . . 

Huron 

Ladoga 

Michigan 

Nicaragua 
Salton Lake 2 . 

Superior 

Tanganyika . . 

Titicaca 

Victoria 

Winnipeg .... 



Square Miles. 

25,000- 

1,000' 

13,200 

8,500- 

170,000 2 

10,000 2 

1,300 



320 

573 

2,300 2 

23,800 

7,000 

22,450 

2,800 



31,200 
14,000' 
12,500 
26,000' 
9,400 



>epth. Altitude 



Feet. 
200 2 
200 

4,500 
135 2 

3,000 2 
20 2 



2,300 
700 2 
210 
50 2 
734 
730 



320 



1,008 
1,200 

900 



Feet. 

50 
- 580 
1,400 

1.(100' 

-84 

1 .000 
7,000 



- 1,300 
9,960 

l._'oo 

581 

55 

581 

108 

-2G7 

602 

2, 1 170 

12.500 

4,000 

710 



1 Approximate; the figures given are from the best authorities, 1 m t vary From the 
measurements of others. Lake Assal is situated in a depression near the GuJf <>f 
Aden. It is the head of a small bay severed from the sea by aeolian sands. It is Fed 
by a small stream that flows from the sea into the lake. The volume of the lake 
represents the balance between inflow and evaporation. 

2 Subject to great variations; the sign — prefixed to the altitude indicates below 
sea-leveL 



VI 

The Ttdes 

The following very clear solution of a much disputed pr< >l >- 
lem is given by Dr. Emerson E. White, author of a scries of 
mathematical text-books. It is only proper to add that no 
theory on the subject fully explains all the phenomena 
noted. Dr. White's solution meets the views of most 
students. 



APPENDIX 



379 



Let E equal the attraction of the earth, and M equal the attraction of 
the moon at B, and M' the attraction of the moon at A and C. 

Since distance OB is less than OA or OC, M > M\ Hence E-M <E 
— M' , and hence the water at B is lighter than at A or C — i.e., has less 
specific gravity, and is lifted or bulged by the surrounding heavier water. 

Let E equal attraction of the earth and m equal attraction of moon at 
B', and m! equal attraction of moon at A' or C. Since distance OB' is 




greater than OA' or OC, m < m' '. Hence E + m < E + m', and hence 
the water at B' is lighter or has less specific gravity than at A' or C and is 
lifted or bulged by the surrounding heavier water. Since distance OB is 
less than OB', M > m, and hence the tide at B is higher than at B'. 



VII 



Table Showing the Number of Grains of Moisture, 
by Weight Necessary to Saturate a Cubic Foot 
of Air at Normal Density 



Tempera- 
ture. 


Moisture in 
One Cubic 
Foot of Air. 


Tempera- 
ture. 


Moisture in 
One Cubic 
Foot of Air. 


Tempera- 
ture. 


Moisture in 

One Cubic 

Foot of Air. 


Degrees F. 
-40 


Grains. 
.08 


Degrees F. 

45 


Grains. 
3.42 


Degrees F. 
68 


Grains. 
7.48 


-30 


.13 


50 


4.08 


70 


7.98 


-20 


.22 


52 


4.37 


72 


8.51 


-10 


.36 


54 


4.69 


74 


9.07 





.56 


56 


5.02 


76 


9.66 


10 


.87 


58 


5.37 


78 


10.28 


20 


1.32 


60 


5.75 


80 


10.94 


30 


1.96 


62 


6.14 


90 


14.79 


35 


2.37 


64 


6.56 


100 


19.92 


40 


2.85 


66 


7.01 


110 


26.43 



ADDITIONAL REFERENCE BOOKS 

Beaches and Tidal Marshes of Atlantic Coast, Shaler. United 
States Geological Survey, Montana. 

Glacial Lake Agassiz, Upham. United States Geological Survey, 
Montana. 

Glacial Gravels of Maine, Stone. United States Geological 
Survey, Montana. 

Lake La Hontan, Russell. United States Geological Survey, Mon- 
tana. 

Rock Scorings of the Ice Age, Chamberlain. United States Geo- 
logical Survey, Seventh Annual Report. 

Lake Bonneville, Gilbert. United States Geological Survey, Mon- 
tana. 

The Henry Mountains, Gilbert. 

Educational Series of Rock Specimens, Dillcr. United States 
Geological Survey Bulletin, $1.50. 

Earth Sculpture, Geikie. G. P. Putnam's Sons. 

Manual of Geology, Dana. American Book Company. 

Elements of Geology, Le Conte. Appleton & Co. 

Common Minerals and Rocks, Crosby. D. C. Heath & Co. 

Glaciers of North America, Russell. Ginn & Co. 

Rivers of North America, Russell. Ginn & Co. 

Lakes of North America, Russell. Ginn & Co. 

The Highest Andes, Fitz Gerald. Charles Scribner's Sons. 

Volcanoes, Hull. Charles Scribner's Sons. 

Sea and Land, Shaler. Charles Scribner's Sons. 

Dawn of History, Keary. Charles Scribner's Sons. 

Earthquakes, Milne. Appleton & Co. 

Deep Sea Soundings and Dredgings, Sigsbee. United Slides Coast 
Survey. 

Island Life, Wallace. Macmillan Company. 

Distribution of Animal and Plant Life, Wallace. 

Elementary Meteorology, Davis. Ginn & Co. 

Geography of Minnesota, Hall. H. W. Wilson Company (St. 
Paul.) 

Climate and Time, Croll. Appleton & Co. 

Man, Past and Present, Keane. Macmillan Company. 

Yellowstone National Park, Chittenden. Robert Clark Company 
(Cincinnati.) 

380 



INDEX 



Adelsberg cavern, 150 

Adirondack Mountains, 165, 354 

^Eolian waste, 227, 229 

Mtna, eruption of, 87 

Agassiz, Lake, 177 

Alluvial cones, 114 

Alpheus River, 147 

Alps, 77, 156 

Amazon River, 130 

Andes Mountains, 72 

Animals, classes of, 321 

distinguished from plants, 307 

regional distribution of, 328 
Anticyclones, 249, 257 
Appalachian Mountains, 61, 76, 81, 

165, 356, 358 
Arctic currents, 209 
Aryan family, 340 

migrations of, 349 
Atlas Mountains, 77 
Atmosphere, 22, 23 

composition of, 214 

density of, 215 

movements of, 216 
Aurora borealis, 274 
Avalanches, 155 
Axis, inclination of, 16 

Bad lands, 67 
Balkan Mountains, 81 
Baltic plain, 63 
Barometer, 217, 252 
Bars, river, 123 
Basalt, 28 
Base level, 111 
Basin region, 364 
Black Hills, 34, 90 
Blizzards, 258 
Block mountains, 74 
Bluffs, river, 359 



Bogs, climbing, 186 

quaking, 187 
Bolsas, 184 
Bonneville, Lake, 181 
Bottom-lands, 5,6, (See Flood-plains) 

California valley, 367 

Calms, 221 

Canoe-shaped valleys, 79 

Cascade Mountains, 74 

Cascades, 125 

Caspian Sea, 47, 64, 175, 180 

Catskill Mountains, 74 

Caverns, 149 

Centrosphere, 22 

Chad, Lake, 175 

Cinder cones, 86, 90 

Cirrus clouds, 236 

Clay, 25 

Clearing showers, 256 

Climate, changes in, 290 

continental, 288 

effects of, altitude, 287 

effects of, latitude, 286 

effects of, ocean currents, 210 

effects of, winds, 289 

zones of, 291 
Cloud banners, 236 

belt, equatorial, 243 
Cloudbursts, 241 
Clouds, formation of, 235, 238 

nomenclature of, 236, 237, 238 
Coal, 36 

production of, 371 
Coasts, changes in elevation of, 4 

fjorded, 4, 54 

forms of, 52, 53 

rising, 4, 56 

sinking, 4, 55 
Cold waves, 257 



381 



382 



INDEX 



Colorado Plateaus, 363 
Columbia River, 126, 129, 174 
Continental plateau, 46 
Continents, 43 
Copper, production of, 372 
Coral formations, 49, 57 
Cordillera, 72 
Coronas, 283 
Corrasion, 111, 115, 119 

rate of, 112 
Crater Lake, 175 
Crevasses, 160 
Cuesta, 63 
Cumulus clouds, 237 
Cyclones, 249, 250, 252, 254 
Cyclonic storms, 243 
Cyclops, 211 

Danube River, 65 
Davis cut-off, 116 
Day and night, IS 
Dead Sea, 47 
Death Valley, 365 
Delta, Adige-Po, 121 

Ganges-Brahmaputra, 65 

Mississippi, 121 

Nile, 65 

Volga, 121 
Delta lands, productivity of, 122 
Deltas, formation of, 121 
Desaguedero River, 132 
Deschutes River, 129 
Deserts, causes of, 296, 299 

distribution of, 298 

winds of, 225, 226 
Dew, 233 

Dew-point, 232, 233 
Divides, 112 

migration of, 127 
Doldrums, 220 
Drowned valleys, 55 
Drumlins, 166 

Earth, form of, 14 

inclination of axis, 16 

motions of, 15 

size of, 15 
Earthquake, Arica, 104 

Babispe, 106 



Earthquake, Charleston, 103, 107 

Lisbon, 104 

New Madrid, 104 

San Francisco, 106 
Earthquakes, causes of, 105 

nature of, 101, 106 

occurrence, 107 
Electricity, laws of, 268 

negative, 269, 270 

of the air, 270 

positive, 269, 270 
Environment, 1, 3, 306, 311, 349 
Equatorial current, 207 
Era, Archaean, 34 

Cenozoic, 37 

Mesozoic, 36 

Paheozoic, 35 
Erosion, 111 
Erratic bowlders, 16S 
Eskers, 166 
Estuaries, 123 

favorable to commerce, 124 
Evaporation, 155 

Fall Line, 63, 357 

Felspar, 28, 30 

Fishes and frogs, showers of, 242 

Fjords, 123 

Flood-plains, 5, 6, 64, 114, 119, 120. 

133 
Floods, river, 129 
Fog, 235 
Forests, 323 

of United States, 370 
Fossils, 33 
Frost, 234 

Ganges River, 121 

Geoid, 14 

Geysers, 142 

Glacial drift. 165 

epoch, 37, 165, 324, 355 

Glaciers, 159, 163, 173 

Gneiss, 32 

Gold, production of, 372 

Graham's Island, origin of, 95 

( Irains, distribution of, 317 

production of United States, 361 
world's production of, 319 



INDEX 



383 



Granite, 29 

Granitic rocks, 27 

Grasses, distribution of, 317 

Gravel, 25 

Great Central Plain, 66, 359 

Great Lakes, 182 

Great Salt Lake, 175, 180, 364 

Gulf Stream, 207, 212 

Hail, 245, 246 
Halos, 283 
Hellgate, 204 
Henry Mountains, 90 
Himalaya Mountains, 74 
Hoang River, 128 
Hornblende, 28 
Horse latitudes, 221 
Howe's Cave, 150 
Hudson River, 123 
Humidity, relative, 232 
Huns, migration of, 347 
Huronian Mountains, 77 
Hurricanes, 250 
Hydrosphere, 22 
Hygrometer, 232 

Ice of the sea, 196 
Icebergs, 162, 197 
Iron ore, production of, 371 
Islands, continental, 48 

coral, 49, 57 

fresh water of, 140 

oceanic, 48 

volcanic, 48 
Isobars, 264 
Isogonics, 278 
Isotherms, 264 
Isostatic balance, 26 

Jura Mountains, 73 

Karnes, 166 

Karabogas, 175 

Kettle holes, 166 

Khaibar Pass, 83 

Kongo River, 131 

Krakatoa, eruption of, 92, 95 

Kuro Siwo, 208 



Laccolites, 90 

Lake Bonneville, 364 

La Hontan, 364 

Superior, iron ores of, 358 
Lakes, accidental, 172 

buried, 179 

destruction of, 177 

distribution of, 182 

finger, 172 

glacial, 171 

lagoon, 173 

marsh, 170 

playa, 176 

salt, 175, 182 

walled, 172 
Land, area of, 42 

average elevation of, 46 

vertical forms of, 60 
Landslides, 157 
La Souffriere, eruption of, 95 
Laurentian Mountains, 77 
Lava, composition of, 91 

flow of, 89, 94 
Life forms, bearings on physiogra- 
phy, 329 

dispersal of, 302, 308, 310, 312 

laws of structure, 304 
Light, reflection of, 282 

refraction of, 281 
Lightning, kinds of, 272, 273 
Limestone, 31 
Lithosphere, 21 
Little Hell, 209 
Llanos, 61, 62 
Loess, 229 
Loop, formation of, 115 

of Mississippi River, 116 
Lost rivers, 146 
"Low," 249 

Lowlands, densely peopled, 6 
Lucrine Lake, 175 
Luray Cavern, 147, 150 

Mackerel sky, 236 
Maelstrom, 204 
Magnetic variation, 276 

storms, 279 
Magnetism, laws of, 275 
Mammoth Cave, 146, 150 



384 



INDEX 



Mankind, classification of, 335 

distribution of, 335, 336, 337, 340 

migrations of, 346 

relations to physiography, 349 
Mariner's compass, 2S0 
Marl, 25 

Mauna Loa, eruptions of, 86, 92 
Mesas, 68 
Meteorites, 10 
Mica, 28 

Middle Atlantic States, 357 
Mineral veins, 149 
Mirages, 282 
Mississippi River, 65, 115, 116, 121, 

130, 131 
Moats, formation of, 115 
Mceris, Lake, 179 
Mohawk Gap, 81 
Monadnock, 72 
Moraines, 161 
Mountains, block, 74 

folded, 71 

nomenclature of, 72 

relict, 77 

physiographic aspect of, 75 

structure of, 73 
Mud flats, 189 

volcanoes, 144 

Natural bridges, 151 
Nebular hypothesis, 10 
New England Plateau, 354 
Niagara Falls, 126 
Nile River, 131 

North America, 34, 35, 36, 37 
North Pole, magnetic, 276 
North Star, 16 

Oases, 298 

Obsidian, 91 

Ocean currents, 204 

Oil, use of, in storm waves, 199 

Ontario, beach of, 182 

Orinoco River, 130 

Oxbows, formation of, 115 

Pacific coast region, 367 
Palisades, 90 
Palmyra Bend, 116 



Pampas, 61 
Peat, 25, 185, 186 
Pel£e, eruption of, 95 
Pele's hair, 89 
Peneplain, 63, 67 
Percolating waters, 138 
Petroleum, production of, 371 
Piedmont lands, 73 
Plains, alluvial, 62 

arctic, 66 

coast, 62 

distribution of, 65 

economic value of, 07 

flood (See Flood-plains) 

lacustrine, 64 

marine, 62 

physiography of, 60 
Planetesmal hypothesis, 11 
Planets, 9, 10 
Plateau, Bolivian, 71 

Iberian, 71 

Iran, 71 

Mexican, 71 

New England, 71 

Pamirs, 70, 77 

Parks, 70 

Tibet, 70 
Plateaus, distribution of, 70 

economic aspect of, 70 

nomenclature of, 68 
Po River, 121 
Polynesia, 48 

Pompeii, destruction of, 95 
Pot holes, 166 
Poudreuses, 157 
Puget Sound, 78 
Pumice-stone, 91 
Pygmies, 342 
Pyrenees Mountains, 81 

Rain, 239 

Rainbows, 284 

Rainfall, abnormal, 241 , 2 12 

cyclonic, 243 

distribution of, 239, 240 

periodical, 241 
Rainless regions, 244 
Red River <.f the North, 64, 118 
Reelfool Late, 104 



INDEX 



385 



Relative humidity, 232 

Relict mountains, 77 • 

Ribbon rock, 149 

Rift, African, 78 

Rivers, antecedent, 117 

consequent, 117 

continental, 132 

development of, 117 

distribution of, 129 

flood-plains of, 6, 119 

infant, 117 

lost, 146 

mature, 117 

old, 119 

sediments of, 114, 120, 123 

terraces of, 128 

underground, 145 

unusual adjustments of, 128 
Rock, heavy strain of, 106 

igneous, 28 

metamorphic, 32 

sedimentary, 29, 31 
Rock envelope, movements of, 25 

structure, 22 
Rock mantle, 24 
Rock waste, 24, 72, 114, 212 

movement of, 191 
Rocking stones, 168 
Rocky Mountains, 34, 64, 72, 363 
Russian Plain, 65 

Salton Lake, 365 
Sand, 25 
Sand dunes, 229 
Sandstone, 29 
Sand valleys, 139 
Sandy hooks, 55, 211 
Santorini, origin of, 95 
Sargasso seas, 210 
Saskatchewan River, 129 
Sea, the, 50 

area of, 50 

arms of the, 51 

color of, 52 

depths of, 51 
Sea ice, nomenclature of, 196 
Seasons, change of, 17, 294 
Sea water, composition of, 193 

specific gravity of, 195 



Sea water, temperature of, 195 

Sediments, 114, 120, 123 

Seismograph, 107 

Seismometer, 107 

Semitic family, 341 

Shenandoah Valley, 78 

Siberian Plain, 65 

Sierra, 72 

Sierra Nevada Mountains, 74 

Silica, 28 

Silt, 114 

Silvas, 62 

Silver, production of, 372 

Sinter, 149 

Slate, 30, 32 

Snow, 154, 244 

crystalline forms of, 245 
Solar system, 9 
Sound Valley, 368 
Sounds, 174 
Sphagnum, 185 
Split Rock, 168 

Springs, nomenclature of, 141, 142 
Stalactites, 151 
Stalagmites, 151 
Steppes, 61 
Storm cards, 253 

tracks, 255 
Storm waters, disposition of,lll,137 
Storms, 249 

land, 254, 256 
Strata, order of, 32 
Stratus clouds, 238 
Stromboli, 86, 88 
St. Elmo's fire, 273 
Suliman Mountains, 74 
Swamp and marshes, 184, 187 

Table-land, 68 

Talus, 75 

Temperature, daily range of, 288 

extremes of, 293 

mean annual, 292 
Textile plants, 323 
Thera, origin of, 96 
Thunder-storms, 272 
Tian Shaw Mountains, 74 
Tidal waves, 104 
Tides, 201 



3S6 



INDEX 



Tides, Bay of Fundy, 204 

bores, 203 
Tigris-Euphrates River, 6 
Titicaca, Lake, 180, 184 
Tornadoes, 259 

Transportation of rock waste, ajolian, 
227 

fluviatile, 114 

glacial, 165 

marine, 210 

tidal, 123 
Trap, 28 
Tufa, 149 
Tulare Lake, 181 
Tundras, 61, 188 
Tuolumne River, 129 
Typhoons, 250 

Uinta Mountains, 71, 73 
Underground waters, 137 
United States, industrial regions of, 
352 
resources of, 370 
Uplift of land, 26, 37, 56 
Utah Lake, 175 

Valleys, intermontane, 73, 81 

nomenclature of, 75, 79 

stream, 78 

transverse, 73, 78 
Vandals, migration of, 347 
Vesuvius, 87, 89, 91 
Vistula River, 128 
Volcanic eruptions, 87, 89 
Volcanoes, distribution of, 96 

Ecuadorean, 92 

Hawaiian, 86, 89, 91 

Icelandic, 94 

Mediterranean, 86, 89, 92 



Volcanoes, Mexican, 97 
nature of, 91 
North American, 97 
structure of, 86 

Warm waves, 258 
"Waterfalls, formation of, 125 
Water gaps, 79, SI 
Watershed, 112 
Waterspouts, 263 
Water vapor, 231 
Waves, 198 

effects of, 200, 211 
Weather bureau, 266 
Weather forecasting, 264 
Weathering processes, 111 
Weir's Cave, 147, 150 
Wells, artesian, 140 

how filled, 139 
White squalls, 263 
Willamette Falls, 127 

Valley, 368 
"Will o' the wisp," 274 
Wind gaps, 127 
Winds, causes of, 217 

day and night, 224 

local desert, 225 

monsoon, 222 

polar, 221 

prevailing westerlies, 220 

roaring forties, 221 

trade, 219 

Yellowstone National Park, 144 
Yosemite Falls, 125 . 
Young River, 117 

Zambesi, Falls of, 125 
Zones, 17, IS, 295 



MAY 30 1908 



